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How to concatenate strings in JavaScript?

Tim Mouskhelichvili
Tim Mouskhelichvili
3 minutes to read

In JavaScript, you have a lot of options when it comes to the concatenation of strings.

You can use:

  1. The + operator.

  2. Template literals.

  3. The built-in concat() function of String.

  4. The built-in join() function of Array.

In this article, I will show you how to use each one of them, as well as the positives and the negatives of each one.

How to concatenate strings in JavaScript?

String concatenation using the + operator

This method is very easy to read and understand, that's why it is the first that you learn in class.

javascriptconst str = 'This is a very long' + ' ' + 'string!';

// OUTPUT: This is a very long string!

You can also use the += operator.

javascriptlet str = 'This is a very long';
str += ' ';
str += 'string!';

// OUTPUT: This is a very long string!

Doing a += b is an abbreviation of doing a = a + b.

If however, you have a lot of strings to concatenate it can quickly become harder to manage.

javascriptconst str = 'This' + ' is' + ' a' + ' very' + ' long' + ' string!';
// OUTPUT: This is a very long string!

This is hard ❌ to read.

Since, the release of ES6, I prefer to use templates strings because they make my code more readable.

JavaScript String Concatenation

String concatenation using templates literals

If your browser supports ES2015, you can use templates literals (or template strings) to concatenate strings.

Template literals are literals that are delimited by backticks (`).

javascriptconst str = 'very long';

// OUTPUT: This is a very long string!
console.log(`This is a ${str} string!`);

Another advantage of using templates literals is your ability to use multiline strings.

is a very long string!`);

You can also do nesting with templates literals.

javascriptconst condition = true;
const str1 = 'very long';
const str2 = 'very little';

console.log(`This is a ${condition ? str1 : str2} string!`);

String concatenation using the concat() function

Another option that you have is to use the concat() function.

It is supported by all browsers.

The concat() function accepts an unlimited number of strings to concat as parameters.

javascript// OUTPUT: This is a very long string!
console.log('This is'.concat(' a ', 'very long', ' string!'));

In my experience, this function is very rarely used. Developers end up using either the + operator or template strings.

JavaScript String Concat Function

String concatenation using the join() function

The final option to concatenate strings is to use the join() built-in function.

This method is interesting when you have a big array of strings that you want to concatenate.

Optionally, you can also specify a separator. By default, it is a comma.

javascript// OUTPUT: This is,a,very long,string!
console.log(['This is', 'a', 'very long', 'string!'].join());

To insert spaces between those strings, just specify the separator.

javascript// OUTPUT: This is a very long string!
console.log(['This is', 'a', 'very long', 'string!'].join(' '));
JavaScript String Join Function

Final Thoughts

As you can see you have a lot of options to concatenate a string.

For my part, I mostly use the template literal for normal cases, and the join() function when I have an array.

Thank you for reading! Please share this article.

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