A method in JavaScript is a function that is a property of an object. When working with strings or arrays, methods allow us to perform useful operations like searching, modifying, or transforming the data.
| Method | Description | Example |
|---|---|---|
| length | Returns the number of characters | 'hello'.length → 5 |
| charAt() | Returns character at index | 'hello'.charAt(1) → 'e' |
| charCodeAt() | Returns UTF-16 code | 'A'.charCodeAt(0) → 65 |
| includes() | Checks if string contains a substring | 'hello'.includes('he') → true |
| startsWith() | Checks if string starts with substring | 'hello'.startsWith('he') → true |
| endsWith() | Checks if string ends with substring | 'hello'.endsWith('lo') → true |
| toUpperCase() | Converts to uppercase | 'hello'.toUpperCase() → 'HELLO' |
| toLowerCase() | Converts to lowercase | 'HELLO'.toLowerCase() → 'hello' |
| slice() | Extracts a section | 'hello'.slice(1,4) → 'ell' |
| substring() | Extracts characters | 'hello'.substring(1,4) → 'ell' |
| replace() | Replaces first match | 'hello'.replace('l', 'x') → 'hexlo' |
| replaceAll() | Replaces all matches | 'hello'.replaceAll('l', 'x') → 'hexxo' |
| trim() | Trims whitespace | ' hello '.trim() → 'hello' |
| trimStart() | Trims start whitespace | ' hello'.trimStart() → 'hello' |
| trimEnd() | Trims end whitespace | 'hello '.trimEnd() → 'hello' |
| split() | Splits string into array | 'a,b,c'.split(',') → ['a','b','c'] |
| concat() | Concatenates strings | 'hello'.concat(' world') → 'hello world' |
| repeat() | Repeats string | 'ha'.repeat(3) → 'hahaha' |
| padStart() | Pads string at start | '5'.padStart(3, '0') → '005' |
| padEnd() | Pads string at end | '5'.padEnd(3, '0') → '500' |
| Method | Description | Example |
|---|---|---|
| length | Returns number of elements | [1,2,3].length → 3 |
| push() | Adds item to end | [1,2].push(3) → [1,2,3] |
| pop() | Removes last item | [1,2,3].pop() → [1,2] |
| shift() | Removes first item | [1,2,3].shift() → [2,3] |
| unshift() | Adds item to start | [1,2].unshift(0) → [0,1,2] |
| concat() | Joins arrays | [1].concat([2,3]) → [1,2,3] |
| join() | Creates string | [1,2].join('-') → '1-2' |
| slice() | Extracts portion | [1,2,3].slice(1,3) → [2,3] |
| splice() | Add/remove elements | [1,2,3].splice(1,1,9) → [1,9,3] |
| indexOf() | First index of item | [1,2,3].indexOf(2) → 1 |
| lastIndexOf() | Last index of item | [1,2,2].lastIndexOf(2) → 2 |
| includes() | Checks presence | [1,2].includes(2) → true |
| reverse() | Reverses array | [1,2,3].reverse() → [3,2,1] |
| sort() | Sorts array | ['b','a'].sort() → ['a','b'] |
| fill() | Fills with value | [1,2,3].fill(0) → [0,0,0] |
| copyWithin() | Copies part within | [1,2,3,4].copyWithin(1, 2) → [1,3,4,4] |
| map() | Creates new array | [1,2].map(x => x*2) → [2,4] |
| filter() | Filters items | [1,2,3].filter(x => x > 1) → [2,3] |
| reduce() | Reduces to value | [1,2,3].reduce((a,b)=>a+b) → 6 |
| forEach() | Loops through items | [1,2].forEach(x => console.log(x)) |
| some() | Checks if any match | [1,2,3].some(x => x > 2) → true |
| every() | Checks if all match | [1,2].every(x => x > 0) → true |
| find() | Finds first match | [1,2,3].find(x => x > 1) → 2 |
| findIndex() | Index of first match | [1,2,3].findIndex(x => x > 1) → 1 |
| flat() | Flattens array | [1,[2,3]].flat() → [1,2,3] |
| flatMap() | Maps and flattens | [1,2].flatMap(x => [x, x*2]) → [1,2,2,4] |