Data types and variables

weakly typed language

Numerical data

whole numbers

fractional numbers

Text data

"string" or

'string' or

"I\"m a string" or

'I\'m a string" or

'I"m a string' or

"I'm a string"

Boolean data

true/false

new Boolean(false) === false (wtf?)

Variables

in-memory data

temporal

case sensitive

reserved words

[a-zA-Z0-9_$]

var firstVariable; // declare
firstVariable = 1; // assign value
alert(firstVariable);
firstVariable = 'hello';
alert(firstVariable);

var secondVariable = 2;
firstVariable = secondVariable;
console.log(firstVariable);
secondVariable = 'world';
console.log(firstVariable); data are copied on assignment

Calculations

MATH built-in object

var sum = 1 + 2 + 4 + 5;
sum += 20;
sum *= 5;
sum /= 9;
sum -= 1;

String operations

var str = 'Hello ' + 'world';
var name = prompt("Your name is", "unknown");
alert('Hello, ' + name);
document.write('Hello, ' + name); // document?

alert ("I'm " + 26 + " years old");

Arrays

more than one item of data at the same time

zero-based indexing!

var myArray = [];
myArray[0] = 'Hello';
myArray[1] = 'World';
myArray[2] = 1500;

var myArray2 = ['how', 'are', 'you'];

Decisions

Comparison operators

>, <, >=, <=, ===, ==, !=, !==

var bigEnough = 1000 > 1;

If

if (1000 > 1) {
    alert('Big enough');
}

var x = 0;
var y = x > 0 ? 'positive' : 'negative';
console.log(y);

logical operators

• AND &&
• OR ||
• NOT !

t && t -> true

t && f -> false

f && t -> false

f && f -> false

t || t -> true

t || f -> true

f || t -> true

f || f -> false

!t -> f

!f -> t

!!t -> t

!!f -> f

if (condition1) {
   statement1
} else if (condition2) {
   statement2
}
else if (condition3) {
   statement3
}
...
else {
   statementN
}

Switch

switch (expression) {
  case value1:
    //Statements executed when the result of expression matches value1
    [break;]
  case value2:
    //Statements executed when the result of expression matches value2
    [break;]
  ...
  case valueN:
    //Statements executed when the result of expression matches valueN
    [break;]
  default:
    //Statements executed when none of the values match the value of the expression
    [break;]
}

Loops

For

for ([initialization]; [condition]; [final-expression]) {
   statement
}

for (var i = 0; i <= 9; i++) {
   console.log(i);
   // more statements
}

var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

for (var len = arr.length - 1; len >= 0; len -= 1) {
  console.log('index: ', len);
  console.log('value: ',arr[len]);
}

While

unknown number of iterations

while (condition) {
  statement
}

var n = 1000,
    x = 0;

while (n > 0) {
    x += n;
    n -= 1;
}

Do...while

executes at least once

do {
   statement
} while (condition);

var i = 0;
do {
   i += 1;
   console.log(i);
} while (i < 0);

Break and Continue

exit the loop prematurely

var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

for (var i = 0, len = arr.length; i < len; i +=1) {
    if (arr[i] % 2 > 0) {
      break;
    }

    console.log(arr[i]);
    console.log(arr[i]/2);
}

var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

for (var i = 0, len = arr.length; i < len; i +=1) {
    if (arr[i] % 2 > 0) {
      continue;
    }
    console.log(arr[i]);
    console.log(arr[i]/2);
}

Functions

parameters

return values

function scope

function name([param[, param[, ... param]]]) {
   statements
}

name([param[, param[, ... param]]]) // function call