JavaScript String Concat() Method

Summary: in this tutorial, you’ll learn how to use the JavaScript concat() method to concatenate strings.

Introduction to the JavaScript String concat() method

The String.prototype.concat() method accepts a list of strings and returns a new string that contains the combined strings:

string.concat(str1, [...strN]);Code language: JavaScript (javascript)

If the arguments are not strings, the concat() converts them to strings before carrying the concatenation.

It’s recommended that you use the + or += operator for string concatenation to get better performance.

Let’s take some examples of using the concat() method.

1) Concatenating strings

The following example uses the concat() method to concatenate strings:

let greeting = 'Hi';
let message = greeting.concat(' ', 'John');

console.log(message);Code language: JavaScript (javascript)

Output:

Hi JohnCode language: JavaScript (javascript)

2) Concatenating an array of strings

The following example uses the concat() method to concatenate strings in an array:

let colors = ['Blue',' ','Green',' ','Teal'];
let result = ''.concat(...colors);

console.log(result);Code language: JavaScript (javascript)

Output:

Blue Green TealCode language: JavaScript (javascript)

Note that the ... before the colors array argument is the spread operator that unpacks elements of an array.

3) Concatenating non-string arguments

This example concatenates numbers into a string:

let str = ''.concat(1,2,3);

console.log(str);Code language: JavaScript (javascript)

Output:

123Code language: JavaScript (javascript)

In this example, the concat() method converts the numbers 1, 2, and 3 to the strings before concatenating.

Summary

• The concat() method concatenates a string list and returns a new string that contains the combined strings.
• Use + or += operator to concatenate strings for better performance.