Java Script cheatsheet

Including JavaScript in HTML Pages

<script type="text/javascript" src="cheatsheet.js">
  JS code Here
</script>

Attaching an external JS file

<script src="app.js">

Comments

// Single line comment
//* Multi line comment */

Variables

var = can be reassigned but only within the scope of the function.
let = can be reassigned but not re-declared.
const = cannot be reassigned.

Data Types

1.String - "Hello World"
2.Number - 123
3.Boolean - true or false
4.Object - {name: "John", age: 34}
5.Array - [1, 2, 3, 4]
6.Function - function myFunction() { }
7.Undefined - var x;
8.Null - var x = null;
9.Symbol - Symbol( "something" );

Arrays

var myArray = ["John", "Mary", "Peter", "Sally"];
var fruits = ["Apple", "Banana", "Orange", 1,2,3];

Arrays Methods

1.push() - adds an element to the end of an array
2.pop() - removes the last element of an array
3.shift() - removes the first element of an array
4.unshift() - adds an element to the beginning of an array
5.splice() - removes elements from an array
6.slice() - copies elements from an array
7.indexOf() - returns the index of an element in an array
8.join() - joins all elements of an array into a string
9.sort() - sorts the elements of an array
10.reverse() - reverses the order of the elements of an array
11.concat() - joins two or more arrays
12.map() - creates a new array by performing a function on each element of an array
13.toString() - converts an array to a string
14.every() - tests whether all elements in an array pass a test
15.some() - tests whether some elements in an array pass a test
16.lastIndexOf() - returns the last index of an element in an array
17.filter() - creates a new array with all elements that pass a test

Functions

function myFunction(parameter1, parameter2) {
  // code goes here
}

Operators

1.Arithmetic Operators
  + - * / %
2.Comparison Operators
  == != === !== > < >= <=
3.Logical Operators
  && || !
4.Assignment Operators
  = += -= *= /= %=
5.Bitwise Operators
  & | ^ ~ << >> >>>

If Statements

if (condition) {
  // return code here
} else {
  // return code here
}

Loops

for loop
  for (before loop; condition; after loop) {
    // code here
  }

while loop
  initialization;
    while (condition for loop) {
      // code here
      reintialization;
    }

do while loop
  initialization;
    do {
      // code here
      reintialization;
    } while (condition for loop);