JavaScript join method
last modified April 4, 2025
In this article we show how to convert arrays to strings using the
join method in JavaScript.
Array joining
The join method creates and returns a new string by concatenating
all elements in an array. By default, elements are separated by commas, but you
can specify any separator.
This method is useful when you need to convert array data into a formatted
string for display or storage. The original array remains unchanged as
join does not modify the array it's called on.
If the array has only one item, that item will be returned without using the separator. For empty arrays, an empty string is returned. All array elements are converted to strings during the joining process.
Basic join example
The following example demonstrates the basic usage of the join
method.
const fruits = ['apple', 'banana', 'orange']; const result = fruits.join(); console.log(result); console.log(fruits); // Original array remains unchanged
We create an array of fruits and join them into a string. Without a separator argument, the elements are joined with commas. The original array remains unmodified.
$ node main.js apple,banana,orange [ 'apple', 'banana', 'orange' ]
Joining with a custom separator
The join method accepts a separator string as its parameter.
const colors = ['red', 'green', 'blue'];
const spaceSeparated = colors.join(' ');
const dashSeparated = colors.join('-');
console.log(spaceSeparated);
console.log(dashSeparated);
We join array elements with different separators. The first join uses a space, while the second uses a dash. Any string can be used as a separator.
$ node main.js red green blue red-green-blue
Joining with an empty separator
When an empty string is passed as separator, elements are joined without any characters between them.
const letters = ['J', 'S', 'Q', 'L'];
const concatenated = letters.join('');
console.log(concatenated);
We join array elements with no separator between them. This is useful when you need to concatenate characters or strings into a single continuous string.
$ node main.js JSQL
Joining array of numbers
The join method converts all elements to strings automatically.
const numbers = [1, 2, 3, 4, 5];
const joinedNumbers = numbers.join(' + ');
console.log(joinedNumbers);
console.log(typeof joinedNumbers);
We join an array of numbers with a custom separator. All numbers are converted to strings during the join operation. The result is always a string type.
$ node main.js 1 + 2 + 3 + 4 + 5 string
Joining nested arrays
The join method does not recursively join nested arrays.
const mixedArray = [1, [2, 3], [4, [5, 6]]];
const result = mixedArray.join('|');
console.log(result);
When joining arrays containing nested arrays, the nested arrays are converted to
strings using their toString method. This results in
comma-separated values within the nested arrays.
$ node main.js 1|2,3|4,5,6
Source
Array join - language reference
In this article we have demonstrated how to use the join() method to convert arrays to strings in JavaScript.