JavaScript

What is JavaScript?

JavaScript is a cross-platform, object-oriented scripting language.
It is used to make webpages interactive (e.g., complex animations, clickable buttons, popup menus).
JavaScript can be used for both client-side and server-side applications.

JavaScript in Web Browsers

Client-Side JavaScript:

Extends core JavaScript by adding objects to control the browser and the Document Object Model (DOM).
Allows developers to create dynamic and interactive elements on webpages, such as:
- Manipulating HTML elements.
- Responding to user events (e.g., mouse clicks, form inputs, page navigation).

JavaScript on the Server

Server-Side JavaScript:

Extends core JavaScript for server environments using frameworks like Node.js.
Enables the creation of more advanced web functionalities, such as:
- Real-time collaboration between multiple computers.
- Handling server-side operations like database communication and file manipulation.

Key Features of JavaScript

JavaScript provides a standard library of objects, such as:
- Array, Date, and Math.
It includes a core set of language elements:
- Operators, control structures, and statements.
Can be extended with additional objects for various purposes (client-side or server-side).

Interactivity and Connectivity

In the browser, JavaScript can modify the webpage's DOM dynamically.
Server-side JavaScript (e.g., Node.js) can handle custom requests from client-side scripts, enabling a seamless interaction between client and server.

JavaScript \not = Java

JavaScript	Java
Object-oriented. No distinction between types of objects. Inheritance is through the prototype mechanism, and properties and methods can be added to any object dynamically.	Class-based. Objects are divided into classes and instances with all inheritance through the class hierarchy. Classes and instances cannot have properties or methods added dynamically.
Variable data types are not declared (dynamic typing, loosely typed).	Variable data types must be declared (static typing, strongly typed).
Cannot automatically write to hard disk.	Can automatically write to hard disk.

JavaScript and the ECMAScript Specification

JavaScript is standardized by Ecma International, an association for standardizing information and communication systems.
The standardized version of JavaScript is called ECMAScript.
ECMAScript ensures that JavaScript behaves consistently across all environments that support the standard.

The ECMA-262 and ISO Standards

The ECMAScript standard is documented in the ECMA-262 specification.
ECMA-262 is also approved as an ISO standard (ISO-16262).
The specification is available on the Ecma International website.

What ECMAScript Covers

The ECMAScript specification defines core language features:
- Syntax, types, operators, objects, and control structures.
Does not include the Document Object Model (DOM), which is standardized by the W3C and WHATWG.
The DOM is how HTML documents are exposed to scripts, allowing JavaScript to manipulate web pages.

ECMAScript Specification

vs.

JavaScript Documentation

ECMAScript Specification:

Provides a detailed set of requirements for language implementation (e.g., SpiderMonkey in Firefox, V8 in Chrome).
Intended for developers who implement JavaScript engines, not for script programmers.

JavaScript Documentation

Designed for script programmers.
Focuses on practical aspects of JavaScript relevant to developers.
Covers language features, the DOM, and other web-specific APIs.

Running JavaScript

Recent versions of Firefox, Chrome, Microsoft Edge, and Safari all support the features discussed in this guide.

Introduction to JavaScript Syntax

JavaScript Syntax Influences
- Borrows from Java, C, C++
- Influenced by Awk, Perl, Python
JavaScript is case-sensitive
Uses Unicode character set

Statements and Semicolons

Statements:
- Instructions in JavaScript
- Separated by semicolons (;)
Semicolon Usage:
- Not necessary if statements are on separate lines
- Required when multiple statements are on the same line
Best Practice:
- Always use semicolons to avoid errors
- Automatic Semicolon Insertion (ASI) rules exist

JavaScript Input Elements

Source Text:
- Scanned from left to right
- Converted into input elements: tokens, control characters, etc.
Whitespace:
- Includes spaces, tabs, and newlines
- Considered as whitespace and ignored

Comments in JavaScript

// a one line comment

/* this is a longer,
 * multi-line comment
 */

Comment Behavior:
- Cannot nest block comments
- Comments behave like whitespace and are discarded
Hashbang Comments:
- #!/usr/bin/env node (for specifying a JS engine)

Variable Declarations

// Bindings
var mainAxis = "row";
let i = 10;
const dot = ".";

var: Declares a variable (function/global scope)
let: Declares a block-scoped variable
const: Declares a block-scoped, read-only constant

let mood = "light";
console.log(mood);
mood = "dark";
console.log(mood);

Binding Names

Can be any word, digits, $ and _

but the name must not start with a digit

Variable Scope

Global Scope: Default scope for all script-mode code
Module Scope: For module-mode code
Function Scope: Created with functions
Block Scope: Created with curly braces {} (for let and const)

if (Math.random() > 0.5) {
  const y = 5;
}
console.log(y); // ReferenceError: y is not defined

Variable Hoisting

var declarations are hoisted
let and const declarations are not hoisted to the top of their block
Variables declared with let or const cannot be accessed before declaration

console.log(x); // undefined
var x = 3;

function test() {
  console.log(y); // undefined
  var y = "local value";
}

Global Variables

Global Object:
- In web pages, the global object is window
- Use window.variable or globalThis.variable to access globals
Cross-window Access:
- Access global variables from different windows using parent.variableName

Constants in JavaScript

Cannot change value after assignment
Must be initialized during declaration

const PI = 3.14;
const MY_OBJECT = { key: "value" };
MY_OBJECT.key = "otherValue"; // Allowed

const MY_ARRAY = ["HTML", "CSS"];
MY_ARRAY.push("JAVASCRIPT");
console.log(MY_ARRAY); // ['HTML', 'CSS', 'JAVASCRIPT'];

Environment

The collection of bindings and their values that exist at a given time is called the environment.

var nombre = prompt("Ingrese su Nombre");
var mensaje = `Hola ${nombre}, que hermoso eres`;
console.log(mensaje);
alert(mensaje);

Data Types

Seven data types that are primitives:

Boolean: true and false.
null: A special keyword denoting a null value.
undefined: A top-level property whose value is not defined.
Number: An integer or floating point number.
BigInt: An integer with arbitrary precision.
String: A sequence of characters that represent a text value.
Symbol: A data type whose instances are unique and immutable.

and

Object

Numbers

fixed with 64 bits

// All the following values are Numbers
10
-10
10.2
-10.2

console.log(typeof 10);

//  10 x 10 ^ 2
10e2;
//  -10 x 10 ^ 3
-10e3;

// Operators
10 + 11;
10 - 11;
10 * 20;
13 / 40;
40 % 2;

Operators

Arithmetic Operators: These are used to perform basic mathematical operations.

// Hierarchy of operators
3 + 5 / 2(3 + 5) / 2;

Operators

Operator Hierarchy (Order of Operations): JavaScript follows the standard mathematical order of operations, also known as "PEMDAS" (Parentheses, Exponents, Multiplication and Division, Addition and Subtraction). Operations within parentheses are executed first, followed by division, and then addition.

// Infinity AND -Infinity 
1 / 0; -1 / 0;
// NaN
0 / 0;

Operators

Infinity and -Infinity: In JavaScript, dividing a number by zero results in Infinity or -Infinity, depending on the sign of the number.

NaN (Not-a-Number): This special value represents an undefined or unrepresentable value, particularly in arithmetic operations where the result is not a real number, such as dividing zero by zero.

String

16 bits per string element

// String Values
'I am a String'
"I am a String"
'Scape character \' '
"Scape character \" "
' Multiline
  line 2 '

// Template String

`half of 100 is ${100 / 2}`  // half of 100 is 50

// String Values
"a" + "b";
"a".length;
"abcdefg"[0];
"abcdefg"[3];
"a,b,c,d".split(",");
"   ok   ".trim(); // "OK"

String

//  Boolean Values
true 
false

5 > 2
5 >= 2
3 < 4 
4 <= 4
5 != 5
5 == 5
"5" == 5
5 === 5
"5" !== 5

Boolean

//  Boolean Values
true 
false

null || 2
null && 2

true || false
true && false

!true
!false

NaN == NaN // → false

Boolean

Short-circuiting of logical operators

console.log(null || "user")
// → user
console.log("Agnes" || "user")
// → Agnes

JavaScript Data Type Conversion

Dynamically Typed Language: JavaScript does not require explicit data type declaration.
Automatic Type Conversion: Data types are converted as needed during execution.

let answer = 42;
// No error, type is dynamically changed
answer = "Thanks for all the fish!";

Numbers and the '+' Operator in JavaScript

The + operator can lead to type conversion when used with strings and numbers.
Numeric values are converted to strings in expressions involving +.

x = "The answer is " + 42;  // Result: "The answer is 42"
y = 42 + " is the answer";  // Result: "42 is the answer"
z = "37" + 7;               // Result: "377"

Type Conversion with Other Operators

Operators other than + do not convert numbers to strings.
JavaScript treats operands as numbers where possible.

"37" - 7;  // Result: 30
"37" * 7;  // Result: 259

Converting Strings to Numbers

parseInt(): Converts a string to an integer (whole number).
parseFloat(): Converts a string to a floating-point number (decimal).
Unary Plus (+): Converts a string directly to a number.

parseInt("101", 2);  // Result: 5 (binary to decimal conversion)
"1.1" + "1.1";       // Result: "1.11.1" (string concatenation)
(+"1.1") + (+"1.1"); // Result: 2.2 (number addition)

Array Literals

An array literal is a list of expressions enclosed in square brackets [].
Initializes an array with specified values.
The array's length is set to the number of elements.
Note: An array literal creates a new array object each time it is evaluated.

const coffees = ["French Roast", "Colombian", "Kona"];

Arrays in Different Scopes

Global Scope: Array literal created once when the script loads.
Function Scope: A new array is instantiated every time the function is called.
Note: Array literals create Array objects.

function createArray() {
    const array = ["Item1", "Item2"];
    // New array created on each function call
}

Extra Commas in Array Literals

Extra Commas: Leave empty slots in the array.
Trailing Commas: Ignored in array literals.

const fish = ["Lion", , "Angel"];
// Result: [ 'Lion', <1 empty item>, 'Angel' ]

const myList = ["home", , "school"];
// Length: 3, myList[1] is empty

const myList2 = [, "home", , "school"];
// Length: 4, myList[0] and myList[2] are missing

const myList3 = ["home", , "school", ,];
// Length: 4, myList[1] and myList[3] are missing

Handling Extra Commas

Trailing Commas: Help keep git diffs clean by adding one line for new elements.

const myList = [
  "home",
  "school",
+ "hospital",
];

Expression

// Expressions
10 + 5 <= 10 + 6

Mental Exercise

let x = 10,
    y = "a";

console.log( y === b || x >= 10 );

Which is the result?

Block statement

{
  statement1;
  statement2;
  // …
  statementN;
}

The most basic statement is a block statement, which is used to group statements. The block is delimited by a pair of curly braces

Control Flow

if else
while
for
switch

// IF
if (2 >= 3) {
    console.log(0);
} else {
    console.log(1);
}

if (2 >= 3) {
    console.log(0);
} else if( 4 < 2) {
    console.log(1);
} else {
     console.log(2);
}

switch (prompt("What is the weather like?")) {
  case "rainy":
    console.log("Remember to bring an umbrella.");
    break;
  case "sunny":
    console.log("Dress lightly.");
  case "cloudy":
    console.log("Go outside.");
    break;
  default:
    console.log("Unknown weather type!");
    break;
}

// Loop While
let a = 10;

while (a >= 0) {
    console.log(a);
    a--;
}

// Loop Do While
do {
    console.log(a);
    a++
} while(a <= 10);

for(let i = 0 ; i <= 10 ; i++) {
    console.log(i);
}

// The are other syntax, see the next slides

The following values evaluate to false (also known as Falsy values):

false
undefined
null
0
NaN
the empty string ("")

Exception Handling Statements

Throw Statement: Used to throw an exception.
Try...Catch Statement: Used to handle exceptions thrown by the throw statement.
Exception Types: Various types of objects can be thrown, including:
- ECMAScript exceptions
- DOMException

The `throw` Statement

Purpose: To throw an exception with a specified value.

throw expression;


throw "Error2";       // String type
throw 42;             // Number type
throw true;           // Boolean type
throw {
  toString() {
    return "I'm an object!";
  },
};

The `try...catch` Statement

Purpose: To catch and handle exceptions.

try {
  // Statements to try
} catch (exception) {
  // Statements to handle the exception
}

function getMonthName(mo) {
  mo--; // Adjust month number for array index
  const months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];
  if (months[mo]) {
    return months[mo];
  } else {
    throw new Error("InvalidMonthNo");
  }
}

try {
  monthName = getMonthName(myMonth);
} catch (e) {
  monthName = "unknown";
  logMyErrors(e); // Handle the error
}

The `finally` Block

Purpose: To execute statements after try and catch blocks, regardless of whether an exception was thrown

Executes even if an exception is thrown or not.
Overrides return values and re-thrown exceptions from the catch block.

openMyFile();
try {
  writeMyFile(theData);
} catch (e) {
  handleError(e);
} finally {
  closeMyFile(); // Always executed
}

Nesting `try...catch` Statements

Purpose: To handle exceptions at different levels of the code.
Rules:
- Inner try blocks must have a finally block if they don't have their own catch block.
- The enclosing try...catch statement's catch block handles exceptions if no inner catch block is present.

Utilizing Error Objects

Purpose: To provide detailed information about exceptions.
Properties:
- name: General class of the error (e.g., DOMException).
- message: Detailed error message.

function doSomethingErrorProne() {
  if (ourCodeMakesAMistake()) {
    throw new Error("The message");
  } else {
    doSomethingToGetAJavaScriptError();
  }
}

try {
  doSomethingErrorProne();
} catch (e) {
  console.error(e.name);    // 'Error'
  console.error(e.message); // 'The message'
}

Functions

Functions are fundamental building blocks in JavaScript.
They perform tasks or calculate values.
A function takes input and returns an output.
Functions must be defined in the scope from which they are called.

Defining Functions

Function Declarations: Consist of:

function keyword
Function name
List of parameters in parentheses
Function body in curly braces

Parameters: Passed by value. Changes to objects or arrays inside the function affect the original object or array.

function square(number) {
  return number * number;
}

Function Parameters

Arguments are optional if you pass too many, the extra ones are ignored. If you pass too few, the missing parameters get assigned the value undefined.

function minus(a, b) {
  if (b === undefined) return -a;
  else return a - b;
}

console.log(minus(10));
console.log(minus(10, 5));

function power(base, exponent = 2) {
  let result = 1;
  for (let count = 0; count < exponent; count++) {
    result *= base;
  }
  return result;
}

Function Parameters

Objects: Changes to object properties are visible outside the function.

function myFunc(theObject) {
  theObject.make = "Toyota";
}

const mycar = {
  make: "Honda",
  model: "Accord",
  year: 1998,
};

console.log(mycar.make); // "Honda"
myFunc(mycar);
console.log(mycar.make); // "Toyota"

Function Parameters

Arrays: Changes to array elements are visible outside the function.

function myFunc(theArr) {
  theArr[0] = 30;
}

const arr = [45];
console.log(arr[0]); // 45
myFunc(arr);
console.log(arr[0]); // 30

Function Expressions

Functions can be created using function expressions.
Can be anonymous or named.

const square = function (number) {
  return number * number;
};
console.log(square(4)); // 16

const factorial = function fac(n) {
  return n < 2 ? 1 : n * fac(n - 1);
};
console.log(factorial(3)); // 6

Functions as Arguments

Functions can be passed as arguments to other functions.

function map(f, a) {
  const result = new Array(a.length);
  for (let i = 0; i < a.length; i++) {
    result[i] = f(a[i]);
  }
  return result;
}

const cube = function (x) {
  return x * x * x;
};

const numbers = [0, 1, 2, 5, 10];
console.log(map(cube, numbers)); // [0, 1, 8, 125, 1000]

Conditional Function Definition

Functions can be defined conditionally.

let myFunc;
if (num === 0) {
  myFunc = function (theObject) {
    theObject.make = "Toyota";
  };
}

Function Scope

Scope: Variables defined inside a function are only accessible within that function.
Access: A function can access all variables and functions in its defining scope.

const num1 = 20;
const num2 = 3;
const name = "Chamakh";

function multiply() {
  return num1 * num2;
}

console.log(multiply()); // 60

function getScore() {
  const num1 = 2;
  const num2 = 3;
  function add() {
    return `${name} scored ${num1 + num2}`;
  }
  return add();
}

console.log(getScore()); // "Chamakh scored 5"

Recursion and the Function Stack

Recursion: A function that calls itself. Requires a base condition to stop.
Function Stack: Recursion uses a stack to manage function calls.

Closure

is the combination of a function and the lexical environment within which that function was declared.

A closure is a function that remembers its lexical scope even when it's executed outside of that scope. In simpler terms, it's a function that "remembers" the variables and the environment in which it was created.

function multiplier(factor) {
  return number => number * factor;
}

let twice = multiplier(2);
console.log(twice(5));

Multiply-Nested Functions and Scope Chaining

Scope Chaining: Nested functions can access variables from all containing scopes.
Example: A function inside another can access all variables from its parent functions.

function A(x) {
  function B(y) {
    function C(z) {
      console.log(x + y + z);
    }
    C(3);
  }
  B(2);
}
A(1); // Logs 6

Name Conflicts

When variables or parameters with the same name exist in different scopes, the innermost scope takes precedence.

function outside() {
  const x = 5;
  function inside(x) {
    return x * 2;
  }
  return inside;
}

console.log(outside()(10)); // 20

Private variables: Closures allow you to create variables that are only accessible from within the inner function, simulating the behavior of private variables in object-oriented languages.
Callbacks and events: They are essential for handling callbacks and events in JavaScript, allowing a function to access variables from an outer scope.
Modules: Closures are used to create modules, encapsulating related code and data.
Currying: Currying, a technique for transforming functions with multiple arguments into a sequence of functions with a single argument, relies on closures

Rest Parameters

function min(...numbers) {
  let result = Infinity;
  for (let number of numbers) {
    if (number < result) result = number;
  }
  return result;
}

let words = ["never", "fully"];
console.log(["will", ...words, "understand"]);

Arrow functions

Definition: Arrow function expressions offer a shorter syntax and differ from traditional function expressions.
Characteristics:
- Shorter syntax.
- No own this, arguments, super, or new.target.
- Always anonymous.

Will work more in the next slides

// binding function
function play() {
    console.log("Ta Ta Taaaaaaaaaaaaa");
}    

var scream  = function () {
    console.log("Aaaaahhhh!!")
}; 

var motivate = () => {
    console.log("Just do it!")
}

Arrays

Arrays are a fundamental data structure in JavaScript. They allow you to store multiple items under a single variable name. This makes it easier to manage and work with collections of data.

Creating Arrays

Array literal: This is the most common way to create an array. You simply enclose a comma-separated list of items within square brackets ([]).
Array constructor: The Array() constructor can also be used to create arrays. However, it is generally less common than the array literal syntax.

  const fruits = ['apple', 'banana', 'orange'];
  const numbers = new Array(1, 2, 3, 4, 5);

Accessing Array Elements

You can access individual elements of an array using their index. The index starts from 0, so the first element has an index of 0, the second element has an index of 1, and so on.

const firstFruit = fruits[0];

Array Properties and Methods

Arrays have a number of built-in properties and methods that allow you to perform various operations on them. Here are some commonly used ones:

length: This property returns the number of elements in the array.
push(): This method adds one or more elements to the end of an array and returns the new length of the array.
pop(): This method removes the last element from an array and returns the removed element.
shift(): This method removes the first element from an array and returns the removed element.

Array Properties and Methods

unshift(): This method adds one or more elements to the beginning of an array and returns the new length of the array.
slice(): This method extracts a section of an array and returns a new array containing the extracted elements.
concat(): This method merges two or more arrays and returns a new array containing the elements of all the input arrays.

let list = [2, 3, 5, 7, 11];
list.push(12);  // Add an element in the end of array
console.log(list); 
console.log(list.pop());  // Extract a last element of array
console.log(list); 

list.unshift(1); // Add an element beginning of the array
list.shift(1); // Extract an element beginning of the array

console.log(list.indexOf(2))
console.log(list.slice(2,5));
console.log(list.slice(5));

console.log(list.concat([1,3,4,5]));

const array1 = ['a', 'b', 'c'];

for (const element of array1) {
  console.log(element);
}

For of statement

Date Object in JavaScript

JavaScript doesn't have a native date data type.
The Date object provides methods to work with dates and times.

Creating Date Objects

const now = new Date();
console.log(now); // Outputs the current date and time

const specificDate = new Date('2024-09-01T10:00:00');
console.log(specificDate); // Outputs: Sat Sep 01 2024 10:00:00 GMT...

const dateFromComponents = new Date(2024, 8, 1, 10, 0, 0); // Note: Month is zero-indexed
console.log(dateFromComponents); // Outputs: Sun Sep 01 2024 10:00:00 GMT...

Getting Date Components

const date = new Date();
console.log(date.getFullYear()); // Outputs the current year
console.log(date.getMonth());    // Outputs the current month (0-11)
console.log(date.getDate());     // Outputs the current day of the month

console.log(date.getHours());    // Outputs the current hour
console.log(date.getMinutes());  // Outputs the current minute
console.log(date.getSeconds());  // Outputs the current second

Setting Date Components

const date = new Date();
date.setFullYear(2025);
date.setMonth(11); // December
date.setDate(25);
console.log(date); // Outputs: Thu Dec 25 2025 ...

date.setHours(15);
date.setMinutes(30);
date.setSeconds(45);
console.log(date); // Outputs: Thu Dec 25 2025 15:30:45 GMT...

Formatting Dates

const date = new Date();
console.log(date.toDateString()); // Outputs: Fri Sep 01 2024

console.log(date.toTimeString()); // Outputs: 10:00:00 GMT+0000 (Coordinated Universal Time)

console.log(date.toLocaleDateString()); // Outputs: 9/1/2024 (depends on locale)
console.log(date.toLocaleTimeString()); // Outputs: 10:00:00 AM (depends on locale)

Date Arithmetic

const date = new Date();
const futureDate = new Date(date);
futureDate.setDate(date.getDate() + 10); // Add 10 days
console.log(futureDate); // Outputs: (Date 10 days from now)

const date1 = new Date();
const date2 = new Date('2024-09-01');
const diffInMilliseconds = date2 - date1;
const diffInDays = diffInMilliseconds / (1000 * 60 * 60 * 24);
console.log(diffInDays); // Outputs the difference in days

Handling Timezones

const date = new Date();
console.log(date.toUTCString()); // Outputs date in UTC timezone

console.log(date.toLocaleString()); // Outputs date and time in local timezone

Understanding Regular Expressions in JavaScript

What are Regular Expressions?

A regular expression (regex) is a sequence of characters that forms a search pattern.
Used for string matching and manipulation.
Commonly used for validation, searching, and replacing text.

Basic Syntax of Regular Expressions

Literal Characters:

Matches the exact characters.

const regex = /hello/;
console.log(regex.test("hello world")); // true

Metacharacters:

Characters with special meanings, like ., *, +, ?, ^, $, etc.

Special Characters in Regular Expressions

Dot (.):

Matches any single character except newline.

const regex = /h.llo/;
console.log(regex.test("hello")); // true
console.log(regex.test("hallo")); // true

Special Characters in Regular Expressions

Asterisk (*):

Matches zero or more of the preceding character.

const regex = /ho*/;
console.log(regex.test("hoop")); // true
console.log(regex.test("h")); // true

Character Classes and Sets

Character Classes:

\d matches any digit (0-9).
\w matches any word character (alphanumeric plus underscore).
\s matches any whitespace character.

const regex = /\d/;
console.log(regex.test("There are 3 apples")); // true

Character Classes and Sets

Character Sets:

Defined using square brackets [].
[a-z] matches any lowercase letter.
[A-Z] matches any uppercase letter.

const regex = /[a-z]/;
console.log(regex.test("Hello")); // true

Quantifiers in Regular Expressions

* - Matches 0 or more times.
+ - Matches 1 or more times.
? - Matches 0 or 1 time.
{n} - Matches exactly n times.
{n,} - Matches at least n times.
{n,m} - Matches between n and m times.

const regex = /\d{2,4}/;
console.log(regex.test("123")); // true
console.log(regex.test("1")); // false

Anchors in Regular Expressions

Start (^):
- Matches the start of a string.
End ($):
- Matches the end of a string.

const regex = /^hello/;
console.log(regex.test("hello world")); // true
console.log(regex.test("world hello")); // false

Anchors in Regular Expressions

Matches a word boundary (the position between a word and a non-word character).

const regex = /\bworld\b/;
console.log(regex.test("hello world!")); // true
console.log(regex.test("helloworld")); // false

Groups and Ranges

Grouping:

Parentheses () are used to group expressions.

const regex = /(abc)+/;
console.log(regex.test("abcabc")); // true

Regular Expression Flags

Flags modify the behavior of a regex search:

i: Case-insensitive search.
g: Global search.
m: Multi-line search.

const regex = /hello/i;
console.log(regex.test("Hello")); // true

Useful Regular Expression Methods

test():

Tests for a match in a string. Returns true or false.

const regex = /\d+/;
console.log(regex.test("123")); // true

Useful Regular Expression Methods

match():

Returns an array of matches or null.

const regex = /\d+/g;
console.log("There are 123 and 456".match(regex)); // ["123", "456"]

Useful Regular Expression Methods

replace():

Replaces matched substrings in a string.

const regex = /apples/g;
console.log("I like apples".replace(regex, "oranges")); // "I like oranges"

Examples of Regular Expressions in Action

const regex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
console.log(regex.test("example@example.com")); // true

const regex = /^\d{4}-\d{4}$/; // salvadoren format
console.log(regex.test("123-456-7890")); // true

Objects

An object is a collection of properties, each with a name (or key) and a value

Creating Objects

Object Literals:

Syntax: { key1: value1, key2: value2, ... }

const car = {
  make: "Ford",
  model: "Mustang",
  year: 1969
};

Creating Objects

Constructor Functions:

Define objects using functions and the new keyword.

function Car(make, model, year) {
  this.make = make;
  this.model = model;
  this.year = year;
}
const myCar = new Car("Ford", "Mustang", 1969);

Object Initializers (Object Literals)

{ property1: value1, property2: value2, ... }

Allows for easy object creation.
Properties can be strings, numbers, or variables.
Can use computed properties with square brackets.

const person = {
  name: "John",
  age: 30,
  job: "Engineer"
};

Constructor Functions

Create a template function for an object type.
Use this keyword to define properties.
Useful for creating multiple objects of the same type.
Allows for the encapsulation of object behavior.

function Person(name, age) {
  this.name = name;
  this.age = age;
}
const person1 = new Person("Alice", 25);

Using Object.create()

Creates a new object with the specified prototype object and properties.
Flexibility in object creation.
Allows for inheritance without needing a constructor function.
Syntax:
- Object.create(proto,[propertiesObject])

const animal = {
  type: "Invertebrates",
  displayType() {
    console.log(this.type);
  }
};
const fish = Object.create(animal);
fish.type = "Fishes";
fish.displayType(); // Logs: "Fishes"

Accessing Object Properties

Dot Notation:
- Example: objectName.propertyName
- Usage: Direct and straightforward for most properties.
Bracket Notation:
- Example: objectName["propertyName"]
- Usage: Needed for dynamic properties or properties with special characters.

let person = {
    name: "Néstor",
    lastname: "Aldana",
};

console.log(person.name);
console.log(person.age); // Undefined
person.age = 23; // defined later
person.name = "Nexxtor" // Change value
console.log(person.age);

delete person.age; // Delete a property
console.log(person.age);
console.log("age" in person);  // Age exists in person?
console.log("name" in person); // Name exists in person?

Enumerating Properties

for...in loop for enumerable properties.
Object.keys() returns an array of property names.
Object.getOwnPropertyNames() returns all property names, enumerable or not.

const obj = { a: 1, b: 2 };
for (const key in obj) {
  console.log(key, obj[key]);
}

Properties

Adding Properties:
- Direct assignment: objectName.newProperty = value;
- Dynamic assignment with bracket notation: objectName["newProperty"] = value;
Deleting Properties:
- delete objectName.propertyName;

const myObj = { name: "Alice" };
myObj.age = 25; // Add a property
delete myObj.name; // Delete a property

Inheritance and Prototypes

Inheritance: Objects can inherit properties from other objects (prototypes).
Prototype Chain: Mechanism by which objects inherit properties and methods from their prototype.

function Animal(type) {
  this.type = type;
}
Animal.prototype.speak = function() {
  console.log(`The ${this.type} speaks.`);
};
const cat = new Animal("cat");
cat.speak(); // Outputs: "The cat speaks."

Methods in Objects

Functions that are properties of objects.

Prototype Methods:

Define shared methods for all instances.
Example

const car = {
  make: "Toyota",
  drive() {
    console.log("Driving...");
  }
};

Car.prototype.start = function() {
  console.log("Car started");
};

Using `this` in Objects

this Keyword:

Refers to the object from which a method was called.
Allows methods to access and modify object properties.

const person = {
  name: "Bob",
  greet() {
    console.log(`Hello, my name is ${this.name}`);
  }
};
person.greet(); // Outputs: "Hello, my name is Bob"

function normalize() {
  console.log(this.coords.map(n => n / this.length));
}
normalize.call({coords: [0, 2, 3], length: 5});

Arrow functions and this

let empty = {};
console.log(empty.toString);
console.log(empty.toString());

console.log(Object.getPrototypeOf({}) == Object.prototype);

console.log(Object.getPrototypeOf(Object.prototype));

Mutabilidad

let object1 = {value: 10};
let object2 = object1;
let object3 = {value: 10};

console.log(object1 == object2); // true
console.log(object1 == object3); // false

object1.value = 15;
console.log(object2.value); // 15
console.log(object3.value); // 10

JavaScript’s == operator, it compares objects by identity

Destructuring

const [a, b] = array;
const [a, , b] = array;
const [a = aDefault, b] = array;
const [a, b, ...rest] = array;
const [a, , b, ...rest] = array;
const [a, b, ...{ pop, push }] = array;
const [a, b, ...[c, d]] = array;

const { a, b } = obj;
const { a: a1, b: b1 } = obj;
const { a: a1 = aDefault, b = bDefault } = obj;
const { a, b, ...rest } = obj;
const { a: a1, b: b1, ...rest } = obj;
const { [key]: a } = obj;

let a, b, a1, b1, c, d, rest, pop, push;
[a, b] = array;
[a, , b] = array;
[a = aDefault, b] = array;
[a, b, ...rest] = array;
[a, , b, ...rest] = array;
[a, b, ...{ pop, push }] = array;
[a, b, ...[c, d]] = array;


({ a, b } = obj); // parentheses are required
({ a: a1, b: b1 } = obj);
({ a: a1 = aDefault, b = bDefault } = obj);
({ a, b, ...rest } = obj);
({ a: a1, b: b1, ...rest } = obj);

function phi([n00, n01, n10, n11]) {
  return (n11 * n00 - n10 * n01) /
    Math.sqrt((n10 + n11) * (n00 + n01) *
              (n01 + n11) * (n00 + n10));
}

let {name} = {name: "Faraji", age: 23};
console.log(name);

Class

constructor is a special method for creating and initializing objects created with the class.
Methods are defined inside the class body.

class MyClass {
  constructor(prop1, prop2) {
    this.prop1 = prop1;
    this.prop2 = prop2;
  }

  method1() {
    console.log('This is method 1');
  }

  method2() {
    console.log('This is method 2');
  }
}

Creating an Instance

Use the new keyword to create an instance of a class.
The constructor is called when a new instance is created, initializing the object's properties.

const instance = new MyClass('value1', 'value2');
console.log(instance.prop1); // Output: value1
instance.method1(); // Output: This is method 1

Class Inheritance

extends keyword is used to create a child class.
Child class inherits all methods from the parent class.
Methods can be overridden in the child class.

class Animal {
  constructor(name) {
    this.name = name;
  }

  speak() {
    console.log(`${this.name} makes a noise.`);
  }
}

class Dog extends Animal {
  speak() {
    console.log(`${this.name} barks.`);
  }
}

const dog = new Dog('Rex');
dog.speak(); // Output: Rex barks.

Static Methods

Static methods are called on the class itself, not on instances.
Use the static keyword to define static methods.

class MathUtility {
  static add(a, b) {
    return a + b;
  }
}

console.log(MathUtility.add(5, 10)); // Output: 15

Private Fields and Methods (ES2022)

Private fields and methods are prefixed with #.
They cannot be accessed from outside the class.

class Rectangle {
  #height = 0;
  #width = 0;

  constructor(height, width) {
    this.#height = height;
    this.#width = width;
  }

  #calculateArea() {
    return this.#height * this.#width;
  }

  getArea() {
    return this.#calculateArea();
  }
}

const rect = new Rectangle(10, 5);
console.log(rect.getArea()); // Output: 50
// console.log(rect.#height); // Error: Private field '#height' must be declared in an enclosing class

Getters and Setters

Getters and setters allow you to define how to access and mutate properties.
Use get and set keywords.

Getters and Setters

class Person {
  constructor(name) {
    this._name = name;
  }

  get name() {
    return this._name;
  }

  set name(newName) {
    this._name = newName;
  }
}

const person = new Person('Alice');
console.log(person.name); // Output: Alice
person.name = 'Bob';
console.log(person.name); // Output: Bob

JSON

JSON stands for JavaScript Object Notation.
It is a lightweight data interchange format.
Easy for humans to read and write.
Easy for machines to parse and generate.
Commonly used for transmitting data in web applications.

Notes: JSON is language-independent but uses conventions familiar to programmers of the C family of languages, including C, C++, C#, Java, JavaScript, Perl, Python, and many others.

JSON Syntax Rules

keys must be strings enclosed in double quotes.
Values can be: Strings, Numbers. Objects, Arrays, Booleans (true or false), null.

Notes: JSON syntax is derived from JavaScript object notation syntax but is text-only, making it language-independent and ideal for data exchange.

{
  "key": "value"
}

JSON Data Types

String: "Hello, World!"
Number: 42, 3.14
Object:

["red", "green", "blue"]

{
  "firstName": "John",
  "lastName": "Doe"
}

Array

Boolean: true, false
Null: null

A Simple JSON Example

{
  "name": "Jane Doe",
  "age": 30,
  "isStudent": false,
  "courses": ["Mathematics", "Computer Science"],
  "address": {
    "street": "123 Main St",
    "city": "Anytown",
    "zip": "12345"
  }
}

JSON vs. XML

JSON:
- More readable and compact.
- Easier to parse with JavaScript.
- Data format only (no display).
XML:
- More verbose.
- Can include metadata and namespaces.
- Can be used for both data and document markup.

JSON is typically preferred over XML for data interchange due to its simplicity and ease of use with JavaScript, but XML remains in use for complex documents and when strict validation is needed.

Parsing and Stringifying JSON in JavaScript

const jsonString = '{"name": "John", "age": 25}';
const jsonObject = JSON.parse(jsonString);
console.log(jsonObject.name); // Output: John

const jsObject = { name: "Jane", age: 30 };
const jsonStr = JSON.stringify(jsObject);
console.log(jsonStr); // Output: {"name":"Jane","age":30}

Common Use Cases for JSON

Web APIs: Used to exchange data between client and server.
Configuration Files: Storing settings and configurations.
Data Storage: Storing data in NoSQL databases like MongoDB.
Data Interchange: Sharing data between different systems or applications.

Best Practices with JSON

Ensure JSON is well-formed and valid.
Use meaningful key names and consistent naming conventions.
Avoid deeply nested structures for readability and performance.
Validate JSON input to prevent security vulnerabilities like injection attacks.

Symbols

What are Symbols in JavaScript?

Symbol is a primitive data type introduced in ES6 (ECMAScript 2015).
Represents a unique and immutable identifier.
Primarily used as keys for object properties to ensure uniqueness.

Notes: Unlike other primitive data types, each symbol is unique, even if two symbols have the same description.

Creating Symbols

Symbols are created using the Symbol() function.

The description is optional and used for debugging purposes; it does not affect the symbol's uniqueness.

let mySymbol = Symbol();
let anotherSymbol = Symbol('description');

Properties of Symbols

Unique: No two symbols are the same, even with identical descriptions.
Immutable: Once created, a symbol's value cannot be changed.
Hidden: Symbols are not enumerable in for...in loops.

Symbols provide a way to add unique property keys to objects without risking property name collisions.

Using Symbols as Object Keys

Symbols can be used as unique keys in objects.

Using symbols as object keys helps prevent accidental property overwrites or conflicts with other keys.

const sym1 = Symbol('key1');
const obj = {};
obj[sym1] = 'value1';

console.log(obj[sym1]); // Output: 'value1'

Global Symbol Registry

Symbol.for(): Checks the global symbol registry for a symbol with the given key. If it doesn't exist, it creates a new symbol.
Symbol.keyFor(): Retrieves the key associated with a symbol in the global registry.

const globalSym = Symbol.for('globalKey');
console.log(Symbol.keyFor(globalSym)); // Output: 'globalKey'

Well-known Symbols

JavaScript has several built-in symbols known as well-known symbols.
They are used to change or customize object behaviors.
Examples:
- Symbol.iterator: Defines default iterator for objects.
- Symbol.toStringTag: Customizes the output of Object.prototype.toString.
- Symbol.hasInstance: Customizes behavior of instanceof.
Well-known symbols are often used to implement or extend JavaScript's built-in behavior.

Practical Use Cases for Symbols

Private Properties: Use symbols to create properties that are not accessible through normal property enumeration.
Unique Keys: Prevents accidental property collisions in objects.
Custom Iterators: Use Symbol.iterator to create custom iteration logic.

Symbols offer a way to define unique keys and behaviors that help avoid naming collisions and enable advanced programming patterns.

Limitations of Symbols

Not Enumerable: Symbols are not visible in for...in or Object.keys().
Not Serializable: Symbols are ignored in JSON.stringify().
Limited Browser Support: While modern browsers support symbols, older browsers may require polyfills

These limitations are by design, enhancing security and ensuring that symbols provide unique, non-colliding property keys.

Exercise

Create an object that registers a list (Array) of a person's life events in a single day, and a boolean property to check if that person has had an accident during that day

let day = { 
    events : ["cook", "sleep", "running"],
    accident: false
};

Exercise

Create an array to have a journal of person's life event

let journal = [
  {
   events: ["work", "touched tree", "pizza",
            "running", "television"],
   accident: false
  },
  {
   events: ["work", "ice cream", "cauliflower",
            "lasagna", "touched tree", "brushed teeth"],
   accident: false
  },
  {
    events: ["weekend", "cycling", "break", 
            "peanuts","beer"],
    accident: true
  }
]

Exercise

Create a function to add a daily entry to a journal

let journal = [];

function addEntry(events, accident) {
  journal.push({events, accident});
    /******************************************         
     * Is {events, accident}  shorthand to    *
     * {events: events, accident: accident}   *
     *****************************************/
}

addEntry(["weekend", "cycling", "break", "peanuts", "beer"]
            , true);
addEntry(["weekend", "cycling", "break"], false);

Higher-order functions

Functions that operate on other functions

function repeat(n, action) {
  for (let i = 0; i < n; i++) {
    action(i);
  }
}

let departments = [];
repeat(5, i => departments.push(`Department ${i}`));
console.log({departments}); // Only for get a name of the var

Abstracting

function lessThan(n) {
  return m => m < n;
}
let lessThan10 = lessThan(10);
console.log(lessThan10(4));

function unless(test, then) {
  if (!test) then();
}

unless( 2 > 3, n => console.log("ok"))

Create new functions

["A", "B"].forEach(i => console.log(i));

Array Higher-Order Functions

Exercise

Create a Higher-Order function that filters an array

function filter(array, test) {
  let passed = [];
  for (let element of array) {
    if (test(element)) {
      passed.push(element);
    }
  }
  return passed;
}

filter([1,3,5,6,7,10], e => e % 2 == 0);

Array Higher-Order Functions

console.log([1,3,5,6,7,10].filter(e => e % 2 == 0));

Array Higher-Order Functions

Exercise

Create a Higher-Order function that transforms an array

function map(array, transform) {
  let mapped = [];
  for (let element of array) {
    mapped.push(transform(element));
  }
  return mapped;
}

let cars = [{ brand: "Toyota", year: "1990"},
            { brand: "Dogge", year: "2020"},
            { brand: "Pollito", year: "2018"},];
map(cars, e=> e.brand);

Array Higher-Order Functions

let cars = [{ brand: "Toyota", year: "1990"},
            { brand: "Dogge", year: "2020"},
            { brand: "Pollito", year: "2018"},];
cars.map(e => e.brand);

Array Higher-Order Functions

Exercise

Create a Higher-Order function that reduces an array to one value

function reduce(array, combine, start) {
  let current = start;
  for (let element of array) {
    current = combine(current, element);
  }
  return current;
}

console.log(reduce([1, 2, 3, 4], (a, b) => a + b, 0));

JavaScript

What is JavaScript?

JavaScript in Web Browsers

JavaScript on the Server

Key Features of JavaScript

Interactivity and Connectivity

JavaScript and the ECMAScript Specification

The ECMA-262 and ISO Standards

What ECMAScript Covers

ECMAScript Specification

vs.

JavaScript Documentation

ECMAScript Specification:

JavaScript Documentation

Running JavaScript

Introduction to JavaScript Syntax

Statements and Semicolons

JavaScript Input Elements

Comments in JavaScript

Variable Declarations

Binding Names

Variable Scope

Variable Hoisting

Global Variables

Constants in JavaScript

Environment

Data Types

Numbers

Operators

Operators

Operators

String

String

Boolean

Boolean

Short-circuiting of logical operators

JavaScript Data Type Conversion

Numbers and the '+' Operator in JavaScript

Type Conversion with Other Operators

Converting Strings to Numbers

Array Literals

Arrays in Different Scopes

Handling Extra Commas

Expression

Mental Exercise

Block statement

Control Flow

Exception Handling Statements

The throw Statement

The try...catch Statement

The finally Block

Nesting try...catch Statements

Utilizing Error Objects

Functions

Defining Functions

Function Parameters

Function Parameters

Function Parameters

Function Expressions

Functions as Arguments

Conditional Function Definition

Function Scope

Recursion and the Function Stack

Closure

Multiply-Nested Functions and Scope Chaining

Name Conflicts

Rest Parameters

Arrow functions

Arrays

Creating Arrays

Accessing Array Elements

Array Properties and Methods

Array Properties and Methods

For of statement

Date Object in JavaScript

Creating Date Objects

Getting Date Components

Setting Date Components

Formatting Dates

Date Arithmetic

The `throw` Statement

The `try...catch` Statement

The `finally` Block

Nesting `try...catch` Statements

Using `this` in Objects