JavaScript (js) is a light-weight object-oriented programming language which is used by several websites for scripting the webpages.
| Category | Function Name | Description | Example |
|---|---|---|---|
| Global Functions | eval() | Executes a string of JavaScript code. | eval('2 + 2') |
isNaN() | Checks if a value is NaN (Not-a-Number). | isNaN('hello') // true | |
isFinite() | Determines whether a value is a finite number. | isFinite(123) | |
parseInt() | Parses a string and returns an integer. | parseInt('123') // 123 | |
parseFloat() | Parses a string and returns a floating-point number. | parseFloat('123.45') // 123.45 | |
decodeURIComponent() | Decodes a URI component that was previously encoded. | decodeURIComponent('Hello%20World') | |
encodeURIComponent() | Encodes a URI component (e.g., an individual query parameter). | encodeURIComponent('Hello World') | |
decodeURI() | Decodes a full URI string. | decodeURI('https://www.example.com/?name=John%20Doe') | |
encodeURI() | Encodes a URI string (the whole URL). | encodeURI('https://www.example.com/?name=John Doe') | |
| Math Functions | Math.abs() | Returns the absolute value of a number. | Math.abs(-5) // 5 |
Math.ceil() | Rounds a number UP to the nearest integer. | Math.ceil(4.3) // 5 | |
Math.floor() | Rounds a number DOWN to the nearest integer. | Math.floor(4.7) // 4 | |
Math.round() | Rounds a number to the nearest integer. | Math.round(4.4) // 4 | |
Math.random() | Returns a random number between 0 (inclusive) and 1 (exclusive). | Math.random() | |
Math.max() | Returns the largest of the numbers provided. | Math.max(2, 5, 10) // 10 | |
Math.min() | Returns the smallest of the numbers provided. | Math.min(2, 5, 10) // 2 | |
Math.pow() | Returns the base to the exponent power. | Math.pow(2, 3) // 8 | |
Math.sqrt() | Returns the square root of a number. | Math.sqrt(9) // 3 | |
Math.sin() | Returns the sine of a number (in radians). | Math.sin(Math.PI / 2) // 1 | |
Math.cos() | Returns the cosine of a number (in radians). | Math.cos(Math.PI) // -1 | |
Math.tan() | Returns the tangent of a number (in radians). | Math.tan(Math.PI / 4) // 1 | |
| Array Functions | Array.isArray() | Checks if a value is an array. | Array.isArray([1, 2, 3]) // true |
Array.prototype.push() | Adds one or more elements to the end of an array. | [1, 2].push(3) // [1, 2, 3] | |
Array.prototype.pop() | Removes the last element from an array. | [1, 2, 3].pop() // 3 | |
Array.prototype.shift() | Removes the first element from an array. | [1, 2, 3].shift() // 1 | |
Array.prototype.unshift() | Adds one or more elements to the beginning of an array. | [1, 2].unshift(0) // [0, 1, 2] | |
Array.prototype.concat() | Combines multiple arrays into one. | [1].concat([2, 3]) // [1, 2, 3] | |
Array.prototype.join() | Joins all elements of an array into a single string. | [1, 2, 3].join('-') // "1-2-3" | |
Array.prototype.slice() | Returns a shallow copy of a portion of an array. | [1, 2, 3].slice(1) // [2, 3] | |
Array.prototype.splice() | Adds/removes items from an array at a specific index. | [1, 2, 3].splice(1, 1) // [2] | |
Array.prototype.sort() | Sorts the elements of an array. | [3, 1, 2].sort() // [1, 2, 3] | |
Array.prototype.filter() | Creates a new array with all elements that pass the test in the provided function. | [1, 2, 3].filter(x => x > 1) // [2, 3] | |
Array.prototype.map() | Creates a new array with the results of calling a provided function on every element in the array. | [1, 2, 3].map(x => x * 2) // [2, 4, 6] | |
| String Functions | String.prototype.charAt() | Returns the character at the specified index. | 'Hello'.charAt(1) // 'e' |
String.prototype.concat() | Joins two or more strings and returns a new string. | 'Hello'.concat(' World') // 'Hello World' | |
String.prototype.includes() | Checks if a string contains the specified substring. | 'Hello'.includes('ell') // true | |
String.prototype.indexOf() | Returns the index of the first occurrence of a specified value in a string. | 'Hello'.indexOf('e') // 1 | |
String.prototype.slice() | Extracts a section of a string and returns a new string. | 'Hello'.slice(1, 3) // 'el' | |
String.prototype.split() | Splits a string into an array of substrings. | 'Hello World'.split(' ') // ['Hello', 'World'] | |
String.prototype.toLowerCase() | Converts a string to lowercase. | 'Hello'.toLowerCase() // 'hello' | |
String.prototype.toUpperCase() | Converts a string to uppercase. | 'Hello'.toUpperCase() // 'HELLO' | |
| Object Functions | Object.assign() | Copies all enumerable properties from one or more source objects to a target object. | Object.assign({}, {a: 1}, {b: 2}) // {a: 1, b: 2} |
Object.keys() | Returns an array of the enumerable property names of an object. | Object.keys({a: 1, b: 2}) // ['a', 'b'] | |
Object.values() | Returns an array of the enumerable property values of an object. | Object.values({a: 1, b: 2}) // [1, 2] | |
Object.entries() | Returns an array of key-value pairs of an object. | Object.entries({a: 1, b: 2}) // [['a', 1], ['b', 2]] | |
Object.freeze() | Freezes an object, making it immutable. | Object.freeze({a: 1}) // {a: 1} | |
Object.hasOwnProperty() | Checks if an object has a specified property as its own (not inherited). | {a: 1}.hasOwnProperty('a') // true | |
| JSON Functions | JSON.parse() | Converts a JSON string into a JavaScript object. | JSON.parse('{"a": 1}') // {a: 1} |
JSON.stringify() | Converts a JavaScript object into a JSON string. | JSON.stringify({a: 1}) // '{"a":1}' | |
| DOM Functions | document.getElementById() | Returns the element with the specified ID. | document.getElementById('myId') |
document.querySelector() | Returns the first element that matches a specified CSS selector. | document.querySelector('.myClass') | |
document.createElement() | Creates a new HTML element. | document.createElement('div') | |
element.appendChild() | Adds a node as the last child of an element. | element.appendChild(newNode) | |
element.addEventListener() | Adds an event listener to an element. | element.addEventListener('click', function() {}) |
