How Many Backslashes Do I Need to Represent One Backslash in JavaScript Strings and Regular Expressions?

Escaping Backslashes in Strings

In JavaScript, backslashes play a vital role in both string literals and regular expressions. To include a backslash in a string or regex without triggering its special meaning, it is crucial to double it, using .

Strings

Consider the following string:

var str = "\I have one backslash";

This string starts with a backslash, which acts as an escape character that triggers an escape sequence. The sequence instructs the parser to place an actual backslash in the string.

Regular Expressions

In regular expressions, the backslash is also significant for special characters. To match a single backslash in a regex, you similarly need two:

var rex = /\/;

This regex will find occurrences of a single backslash.

Creating Regular Expressions from Strings

If creating a regular expression using a string, you encounter two levels of escaping:

// Matches *one* backslash
var rex = new RegExp("\\");

The first escapes the backslash in the string, while the second escapes the backslash in the regular expression pattern.

ES2015 Update

ES2015 introduced template literals, tag functions, and the String.raw function, providing a new way to escape backslashes. For instance:

let str = String.raw`\apple`;

This string will contain the characters , a, p, p, l, and e. However, be cautious of using ${ within template literals, as it triggers substitutions.

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