Literal character: a, b

A literal character specifies exactly itself to be matched in the input text.

Syntax#

c

Parameters#

• c
• : A single character that is not one of the syntax characters described below.

Description#

In regular expressions, most characters can appear literally. They are usually the most basic building blocks of patterns. For example, here is a pattern from the Removing HTML tags example:

const pattern = /<.+?>/g;

In this example, ., +, and ? are called syntax characters. They have special meanings in regular expressions. The rest of the characters in the pattern (< and >) are literal characters. They match themselves in the input text: the left and right angle brackets.

The following characters are syntax characters in regular expressions, and they cannot appear as literal characters:

• ^, $
• \
• *, +, ?, {, }
• (, )
• [, ]
• |

Within character classes, more characters can appear literally. For more information, see the Character class page. For example \. and [.] both match a literal .. In v-mode character classes, however, there are a different set of characters reserved as syntax characters. To be most comprehensive, below is a table of ASCII characters and whether they may appear escaped or unescaped in different contexts, where "✅" means the character represents itself, "❌" means it throws a syntax error, and "⚠️" means the character is valid but means something other than itself.

[!NOTE] The characters that can both be escaped and unescaped in v-mode character classes are exactly those forbidden as "double punctuators". See v-mode character classes for more information.

Whenever you want to match a syntax character literally, you need to escape it with a backslash (\). For example, to match a literal * in a pattern, you need to write \* in the pattern. Using syntax characters as literal characters either leads to unexpected results or causes syntax errors — for example, /*/ is not a valid regular expression because the quantifier is not preceded by a pattern. In Unicode-unaware mode, ], {, and } may appear literally if it's not possible to parse them as the end of a character class or quantifier delimiters. This is a deprecated syntax for web compatibility, and you should not rely on it.

Regular expression literals cannot be specified with certain non-syntax literal characters. / cannot appear as a literal character in a regular expression literal, because / is used as the delimiter of the literal itself. You need to escape it as \/ if you want to match a literal /. Line terminators cannot appear as literal characters in a regular expression literal either, because a literal cannot span multiple lines. You need to use a character escape like \n instead. There are no such restrictions when using the {{jsxref("RegExp/RegExp", "RegExp()")}} constructor, although string literals have their own escaping rules (for example, "\\" actually denotes a single backslash character, so new RegExp("\\*") and /\*/ are equivalent).

In Unicode-unaware mode, the pattern is interpreted as a sequence of UTF-16 code units. This means surrogate pairs actually represent two literal characters. This causes unexpected behaviors when paired with other features:

/^[😄]$/.test("😄"); // false, because the pattern is interpreted as /^[\ud83d\udc04]$/
/^😄+$/.test("😄😄"); // false, because the pattern is interpreted as /^\ud83d\udc04+$/

In Unicode-aware mode, the pattern is interpreted as a sequence of Unicode code points, and surrogate pairs do not get split. Therefore, you should always prefer to use the u flag.

Examples#

Using literal characters#

The following example is copied from Character escape. The a and b characters are literal characters in the pattern, and \n is an escaped character because it cannot appear literally in a regular expression literal.

const pattern = /a\nb/;
const string = `a
b`;
console.log(pattern.test(string)); // true

Specifications#

{{Specifications}}

Browser compatibility#

{{Compat}}

See also#

• Character classes guide
• Regular expressions
• Character escape: \n, \u{...}