Built-in type methods are predefined functions associated with various data types like strings, numbers, arrays, objects, and more. These methods provide a way to perform specific operations or manipulations on values of those data types. Here’s an overview of some common built-in type methods in JavaScript:
| # |
Built-in Method |
Description |
Example |
| 1 |
String.length |
Returns the length of a string. |
"Hello".length returns 5 |
| 2 |
String.toUpperCase() |
Converts a string to uppercase. |
"hello".toUpperCase() returns “HELLO” |
| 3 |
String.toLowerCase() |
Converts a string to lowercase. |
"Hello".toLowerCase() returns “hello” |
| 4 |
String.indexOf() |
Returns the index of a substring within a string. |
"apple".indexOf("pl") returns 2 |
| 5 |
String.substring() |
Returns a substring based on specified indices. |
"apple".substring(1, 4) returns “ppl” |
| 6 |
String.split() |
Splits a string into an array of substrings based on a delimiter. |
"apple,banana,orange".split(",") returns [“apple”, “banana”, “orange”] |
| 7 |
String.trim() |
Removes whitespace from both ends of a string. |
" hello ".trim() returns “hello” |
| # |
Built-in Method |
Description |
Example |
| 1 |
Array.push() |
Adds elements to the end of an array. |
let arr = [1, 2]; arr.push(3); modifies arr to [1, 2, 3] |
| 2 |
Array.pop() |
Removes and returns the last element of an array. |
let arr = [1, 2, 3]; let last = arr.pop(); modifies arr to [1, 2], last contains 3 |
| 3 |
Array.shift() |
Removes and returns the first element of an array. |
let arr = [1, 2, 3]; let first = arr.shift(); modifies arr to [2, 3], first contains 1 |
| 4 |
Array.unshift() |
Adds elements to the beginning of an array. |
let arr = [2, 3]; arr.unshift(1); modifies arr to [1, 2, 3] |
| 5 |
Array.concat() |
Combines arrays and returns a new array. |
let arr1 = [1, 2]; let arr2 = [3, 4]; let newArr = arr1.concat(arr2); newArr is [1, 2, 3, 4] |
| 6 |
Array.join() |
Joins array elements into a string using a delimiter. |
let arr = ["apple", "banana", "orange"]; let result = arr.join(", "); result is “apple, banana, orange” |
| 7 |
Array.slice() |
Extracts a section of an array and returns a new array. |
let arr = [1, 2, 3, 4, 5]; let subArr = arr.slice(1, 4); subArr is [2, 3, 4] |
| 8 |
Array.splice() |
Adds or removes elements from an array at a specified index. |
let arr = [1, 2, 3, 4, 5]; arr.splice(2, 2, 6, 7); (Removes 2 elements starting from index 2, then add 6 and 7). Hence we get arr = [1, 2, 6, 7, 5] |
| 9 |
Array.forEach() |
Executes a function for each array element. |
let arr = [1, 2, 3]; arr.forEach(item => console.log(item)); prints each element |
| 10 |
Array.map() |
Creates a new array with the results of calling a function on each element. |
let arr = [1, 2, 3]; let doubled = arr.map(item => item * 2); doubled is [2, 4, 6] |
| 11 |
Array.filter() |
Creates a new array with elements that pass a certain condition. |
let arr = [1, 2, 3, 4, 5]; let even = arr.filter(item => item % 2 === 0); even is [2, 4] |
| 12 |
Array.reduce() |
Applies a function against an accumulator and each element to reduce the array to a single value. |
let arr = [1, 2, 3]; let sum = arr.reduce((accumulator, current) => accumulator + current, 0); sum is 6 |
| # |
Built-in Method |
Description |
Example |
| 1 |
Object.hasOwnProperty() |
Checks if an object has a specific property. |
let person = { name: "Alice", age: 30 }; person.hasOwnProperty("name"); returns true |
| 2 |
Object.keys() |
Returns an array of an object’s own enumerable property names. |
let person = { name: "Alice", age: 30 }; let keys = Object.keys(person); keys is [“name”, “age”] |
| 3 |
Object.values() |
Returns an array of an object’s own enumerable property values. |
let person = { name: "Alice", age: 30 }; let values = Object.values(person); values is [“Alice”, 30] |
| 4 |
Object.entries() |
Returns an array of an object’s own enumerable property key-value pairs. |
let person = { name: "Alice", age: 30 }; let entries = Object.entries(person); entries is [[“name”, “Alice”], [“age”, 30]] |
| 5 |
Object.assign() |
Copies the values of all enumerable properties from one or more source objects to a target object. |
let target = {}; let source = { name: "Alice", age: 30 }; Object.assign(target, source); target is { name: “Alice”, age: 30 } |
| 6 |
Object.toString() |
Returns a string representation of an object. |
let person = { name: "Alice", age: 30 }; let str = Object.toString(person); str is “[object Object]” |
These are just a few examples of built-in type methods in JavaScript. JavaScript’s standard library provides a rich set of methods for manipulating various data types, making it easier to work with strings, numbers, arrays, objects, and other built-in types.