JavaScript Array join() Method

The Array.join() method is a built-in JavaScript function used to join all elements of an array into a single string. The elements are separated by a specified delimiter or a comma (,) if no delimiter is provided.

Syntax

arr.join(separator);

Parameters

Return Value

The join() method returns a string containing all array elements joined by the specified separator. If the array is empty, it returns an empty string.

Example 1: Joining Array Elements with Default Separator

let arr = ['HTML', 'CSS', 'JavaScript'];
let result = arr.join();
console.log(result); 
// Output: 'HTML,CSS,JavaScript'

The default separator (a comma) is used to join the array elements.

Example 2: Joining with a Custom Separator

let arr = ['HTML', 'CSS', 'JavaScript'];
let result = arr.join(' - ');
console.log(result); // Output: 'HTML - CSS - JavaScript'

Example 3: Joining an Array of Numbers

let arr = [10, 20, 30, 40, 50];
let result = arr.join(' | ');
console.log(result); 
// Output: '10 | 20 | 30 | 40 | 50'

Example 4: Joining an Empty Array

let arr = [];

let result = arr.join();
console.log(result); // Output: ''

Example 5: Handling undefined and null Values

let arr = [1, undefined, null, 4];

let result = arr.join(' - ');
console.log(result); 
// Output: '1 -  -  - 4'

Example 6: Joining with No Separator

let arr = ['A', 'B', 'C'];

let result = arr.join('');
console.log(result); // Output: 'ABC'

Example 7: Joining Nested Arrays

let arr = [1, [2, 3], 4];

let result = arr.join();
console.log(result); // Output: '1,2,3,4'

Supported Browsers