introduction to javascript

var app = function () {
    return { 
        func: function (f, range, multipliesOf, modifiers) {
            var ret = [];
            for (var i = range.from; i <= range.to; i++) {
                if (i % multipliesOf === 0) {
                    ret.push(f(i)); 
                }
            }
            return ret;
        }
    }
};var result = app().func(function (x) { return x * x }, 
   {from: 1, to: 50}, 2);

result[2] = result[0] + result[1]; // modify array element
var answer = result[2] * 2 + 2;
console.log(answer);

• JavaScript is 18 years old (released in 1995)
• Developed by Brendan Eich at Netscape 
• Was initially named "Mocha", then "LiveScript"
• Has basically very little to do with Java

• Interpreted (vs compiled)
• Dynamically typed (vs static typed, e.g. Java, C++)
• Functional - functions are first class citizens 
  
• Prototype inheritance - inherit from an object not a class

• Create an HTML file and put your code in a <script></script> tag, then open that HTML file in a browser
• Using Chrome / FileFox go to http://repl.it/languages/JavaScript
  
• Open the chrome JavaScript console (we'll use this one)

1 + 1; 

2 

var x = 3; 

enter: 

x * x; 

9  

var part1 = "Hello"; 

var part2 = "World"; 

var full = part1 + " " + part2; 

"Hello World" 

• String ("Hello World")
• Boolean (true, false)
• Number (1, 0.5)

 var x = 2; // everything after "//" is ignored on the same line 

var x = 2; /* now I can write my comment on multiple lines JavaScript code is also ignored x = 3; */console.log(x); //still 2

if (something is true) {
  //then part
} else {
  //else part
} 

 if( 5 > 3) {   console.log("five is greater than three"); }

var x = true; //true and false are reserved keywords in JavaScriptvar y = (1 + 2 == 3); //y is equal to true, as 1 + 2 equals to 3var z = 2 < 1; // z is equal to false, as 2 is not less than 1

var x = true && true; // x will be equal to true as both left AND right = truevar y = true || false; 
// y will be equal to true as either left OR right are true

• AND (true if both operands are true) - &&
• OR (true if either operands is true) - ||
• NOT (changes true to false and false to true) - !
• EQUALS (true if both sides are the same) - == / ===*
• NOT EQUALS (true if both sides are different) - !=
  
• LESS THAN (true if left is less than right) - <
• GREATER THAN (true if left is greater than right) - > 
• LESS THAN OR EQUAL (same as < OR ==) - <=
• GREATER THAN OR EQUAL (like > OR ==) - >= 

var x = (true && true) || false;var y = (1 >= 0) || x == !false;if (!x || (y != false)) {  console.log("condition is true");} else {  console.log("condition is false");}

var x = (true && true) || false;

var y = (1 >= 0) || x == !false;

!true || (true != false)

while (condition is true) {
  //keeps running until condition is false or a call to "break" 
} 

var i = 0; //initialization while (i < 10) { //condition
  i++; //increment
}

for (initialization; condition; increment) {}

1. initialization - happens only once
   
2. condition - before each iteration
   
3. increment - after each iteration
   

var counter = 0;while (true) {   if (counter == 10){    break; // when counter reaches 10, the loop will end  }  counter += 1;}

for (var i = 1; i <= 100; i++) {  //read: if the remainder of i divided by 3 is 0, i.e. a multiple of 3
  if (i % 3 == 0) {    continue; // then stop this iteration and move to the next one   }  console.log(i);}

var myArray1 = new Array(); // empty arrayvar myArray2 = new Array(1,2,3); array with elements 1 2 3

var array = ["a", "b", "c"];console.log( array[0] ); //will print "a"console.log( array[1] ); //will print "b"
console.log( array[2] ); //will print "c"

var array = [];array[0] = "a";array[1] = "b";
array[2] = "c";
//array contains ["a", "b", "c"]

var languages = ["JavaScript", "C++", "Erlang"];// let's change "Erlang" to "Java"// "Erlang" is in the 3rd place, but we count from 0, so it's index 2languages[2] = "Java";console.log(languages);// this will print ["JavaScript", "C++", "Java"]

var myArray = [1,2,3];console.log( myArray.length ); //prints 3

 var myMixedArray = ["Strings", true, false, 1, 2.4];

var myMatrix = [[1,2,3],[4,5,6],[7,8,9]];console.log(myMatrix[0]); //prints [1,2,3]console.log(myMatrix[1]); //prints [4,5,6]
var innerArray = myMatrix[2]; //innerArray = [7,8,9]console.log(innerArray[0]); //prints 7console.log(innerArray[1]); //prints 8
console.log(myMatrix[1][0]); //prints 4 - why? myMatrix[1]=[4,5,6]

var myArray = [1,2,3];for(var i = 0; i < myArray.length ; i++){  var curElement = myArray[i];  console.log("Array element at index " + i + " is " + curElement);}

var myArray = [1,2,3];for(var i in myArray){  if (myArray.hasOwnProperty(i)){ //will be explained in future session    var curElement = myArray[i];    console.log("Array element at index " + i + " is " + curElement);  }}

 var myObject = new Object();

var myObject = new Object();myObject.firstName = "John";myObject.lastName = "Doe";

// : instead of = and , instead of ;
var myObject = { firstName: "John", lastName: "Doe" }

var myObject = {   firstName: "John",   lastName: "Doe",   emails: ["john.doe@gmail.com", "jdoe@example.com"], 
  address: {    line1: "1 Main st.",      city: "New York",  
    state: "NY",  
    zip: 10001  
  }}

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

function foo() {    console.log("No params, no return value"); }function bar(x) {   console.log("Param is " + x + " no return value"); }
function add(x, y) {   return x + y; }

function square(x) { return x*x;}square(2); //-> square(2){ return 2*2 } -> square(2){ return 4 } -> 4

function add(x, y) { return x + y; }function square(x) { return x * x; }
add(square(2), square(3));add(2 * 2, 3 * 3);add(4, 9);
4 + 9;
13;

// filter array to keep only items for which the predicate returns truefunction filter(array, predicate) {   var result = [];   for(var i = 0; i<array.length; i++){    var element = array[i];    if (predicate(element)) result.push(element);  }
  return result;}function isLargerThan3(x) { return x > 3; }filter([1,2,3,4,5], isLargerThan3); //returns [4,5]

// filter array to keep only items for which the predicate returns true
function filter(array, predicate) { 
  var result = []; 
  for(var i = 0; i<array.length; i++){
    var element = array[i];
    if (predicate(element)) result.push(element);
  }
  return result;
}

filter([1,2,3,4,5], function (x) { return x > 3; }); //returns [4,5]

var app = function () {
    return { //return an object with key "func", and a function value
        func: function (f, range, multipliesOf, modifiers) {
            var ret = [];
            for (var i = range.from; i <= range.to; i++) {
                if (i % multipliesOf === 0) {
                    ret.push(f(i)); //add items to an array 
                }
            }
            return ret;
        }
    }
};var result = app().func(function (x) { return x * x }, 
   {from: 1, to: 50}, 2);

result[2] = result[0] + result[1]; // modify array element
var answer = result[2] * 2 + 2;
console.log(answer);