How Do I Properly Escape Backslashes in JavaScript Strings and Regular Expressions?

Single Backslashes in Strings: A Comprehensive Guide

In JavaScript, using a single backslash within a string can be tricky due to its special meaning in both strings and regular expressions. To obtain an actual backslash within a value, it's necessary to employ escape sequences.

Escaping Backslashes in Strings

In JavaScript string literals, to include a literal backslash, use double backslashes (). For example:

var str = "\I have one backslash";

In this scenario, the first backslash acts as an escape character, indicating that the following character should be treated literally. Consequently, the variable str will contain a string with a single backslash.

Escaping Backslashes in Regular Expressions

Regular expressions also make use of backslashes, so it's essential to distinguish between actual backslashes and escape sequences. To match a literal backslash in a regular expression, employ double backslashes ().

var rex = /\/;

Creating Regular Expressions from Strings

When creating a regular expression from a string, two levels of escaping are involved: string literals and regular expression patterns. For instance, to match a single backslash using a string-created regular expression:

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

The first two backslashes escape a backslash in the string literal, while the second two backslashes create the desired escape sequence within the regular expression pattern.

ES2015 Update: String.raw and Template Literals

In ES2015, template literals provide an alternative way to include literal backslashes without extra escaping.

// Using String.raw
let str = String.raw`\apple`;

Caution:

Substitute expressions (${}) cannot be used within template literals containing literal backslashes, as they alter the literal behavior.

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