How to Replace Spaces with Underscores in JavaScript

Replacing Spaces with Underscores in JavaScript #

Use the String.replaceAll method to replace all spaces with underscores in a JavaScript string, e.g. string.replaceAll(' ', '_'). The replaceAll method returns a new string with all whitespace characters replaced by underscores.

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// Not Supported in IE 6-11
const str = 'a very long string';
const strUnderscores = str.replaceAll(' ', '_');

console.log(strUnderscores); // 👉️ a_very_long_string

We called the String.replaceAll method with 2 parameters - the string to be replaced and the replacer string.

The String.replaceAll method is not supported in Internet Explorer. If you have to support the browser, use the String.replace method instead.

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// Supported in IE 6-11
const str = 'a very long string';
const strUnderscores = str.replace(/ /g, '_');

console.log(strUnderscores); // 👉️ a_very_long_string

In the code snippet, we use the String.replace method, passing it a regular expression as the first parameter and a replacer string as the second.

The regular expression / / matches a whitespace character.

We have added the g (global) flag to the regex, which makes the regular expression match all whitespace characters in the string, instead of just the first one.