JavaScript Cheat Sheet: Arrays, Functions, Objects & More

JavaScript Cheat Sheet

JavaScript Arrays

var cars = ["Mercedes", "Tesla","Volvo"];

• pop(): Removes the last element of an array.
• push(): Adds a new element at the end of an array.
• concat(): Joins various arrays into a single array.
• reverse(): Reverses the order of elements in an array.
• indexOf(): Returns the first index of a given element in an array.
• lastIndexOf(): Returns the last index of a given element in an array.
• join(): Combines elements of an array into a single string.
• sort(): Sorts array elements based on a condition.

Global Functions

These functions are built-in to every browser that runs JavaScript:

• parseFloat(): Parses the argument and returns a floating-point number.
• parseInt(): Parses the argument and returns an integer.
• Number(): Returns a number converted from the argument.
• eval(): Evaluates JavaScript code represented as a string.

String Methods

• toLowerCase(): Converts a string to lowercase.
• toUpperCase(): Converts a string to uppercase.
• charAt(): Returns the character at a specific index of a string.
• match(): Retrieves matches of a string against a provided pattern.
• indexOf(): Provides the index of the first occurrence of text in a string.
• lastIndexOf(): Provides the index of the last occurrence of text in a string.

Node Properties

• attributes: Returns a live list of attributes of an element.
• childNodes: Returns a list of child nodes of an element.
• firstChild: Returns the first child node of an element.
• lastChild: Returns the last child node of an element.
• nextSibling: Returns the next node at the same level in the DOM tree.
• parentNode: Returns the parent node of an element.
• previousSibling: Returns the previous node at the same level in the DOM tree.

Node Methods

• appendChild(): Adds a new child node as the last child of an element.
• getFeature(): Returns an object that implements the APIs of a feature.
• hasAttributes(): Returns true if an element has attributes, otherwise false.
• hasChildNodes(): Returns true if an element has child nodes, otherwise false.

JavaScript Data Transformation

map() Method:

var arr = [10,20,30]; var triple = arr.map(x => x * 3); triple; // [30,60,90]

filter() Method:

var arr = [13,40,47]; var odd = arr.filter(x => x % 2); odd; // [13,47]

JavaScript Date Objects

• Date(): Returns a new date object with the current date and time.
• getDay(): Returns a number (0-6) representing the day of the week.
• getFullYear(): Returns the year as a four-digit number (yyyy).
• getHours(): Returns the current hour (0-23).

const d = new Date();

JavaScript Browser Objects

• pageXOffset: Pixels scrolled horizontally from the left of the page.
• pageYOffset: Pixels scrolled vertically from the top of the page.
• document: Returns the document object of the window.
• screen: Returns the screen object of the window.
• screenLeft: Horizontal coordinate of the window relative to the screen.
• screenTop: Vertical coordinate of the window relative to the screen.
• top: Returns the topmost browser window.
• screenX: Same as screenLeft, but required by some browsers.
• screenY: Same as screenTop, but required by some browsers.