Core API

Highlight.js exports a few functions as methods of the hljs object.


highlight(code, {language, ignoreIllegals})

Core highlighting function. Accepts the code to highlight (string) and a list of options (object). The language parameter must be present and specify the language name or alias of the grammar to be used for highlighting. The ignoreIllegals is an optional parameter that when true forces highlighting to finish even in case of detecting illegal syntax for the language instead of throwing an exception.

Returns an object with the following properties:

  • language: language name, same as the name passed in languageName, returned for consistency with highlightAuto

  • relevance: integer value representing the relevance score

  • value: HTML string with highlighting markup

  • top: top of the current mode stack

  • illegal: boolean representing whether any illegal matches were found

  • code: the original raw code


highlightAuto(code, languageSubset)

Highlighting with language detection. Accepts a string with the code to highlight and an optional array of language names and aliases restricting detection to only those languages. The subset can also be set with configure, but the local parameter overrides the option if set.

Returns an object with the following properties:

  • language: detected language

  • relevance: integer value representing the relevance score

  • value: HTML string with highlighting markup

  • secondBest: object with the same structure for second-best heuristically detected language (may be absent)



Applies highlighting to a DOM node containing code.

This function is the one to use to apply highlighting dynamically after page load or within initialization code of third-party JavaScript frameworks.

The function uses language detection by default but you can specify the language in the class attribute of the DOM node. See the scopes reference for all available language names and scopes.


Applies highlighting to all elements on a page matching the configured cssSelector. The default cssSelector value is 'pre code', which highlights all code blocks. This can be called before or after the page’s onload event has fired.


Returns a new instance of the highlighter with default configuration.



Configures global options:

  • classPrefix: a string prefix added before class names in the generated markup, used for backwards compatibility with stylesheets.

  • languages: an array of language names and aliases restricting auto detection to only these languages.

  • languageDetectRe: a regex to configure how CSS class names map to language (allows class names like say color-as-php vs the default of language-php, etc.)

  • noHighlightRe: a regex to configure which CSS classes are to be skipped completely.

  • cssSelector: a CSS selector to configure which elements are affected by hljs.highlightAll. Defaults to 'pre code'.

  • ignoreUnescapedHTML: do not log warnings to console about unescaped HTML in code blocks

  • throwUnescapedHTML: throw a HTMLInjectionError when highlightElement is asked to highlight content that includes unescaped HTML

Accepts an object representing options with the values to updated. Other options don’t change

  noHighlightRe: /^do-not-highlightme$/i,
  languageDetectRe: /\bgrammar-([\w-]+)\b/i, // for `grammar-swift` style CSS naming
  classPrefix: ''     // don't append class prefix
                      // … other options aren't changed


registerLanguage(languageName, languageDefinition)

Adds new language to the library under the specified name. Used mostly internally.

  • languageName: a string with the name of the language being registered

  • languageDefinition: a function that returns an object which represents the language definition. The function is passed the hljs object to be able to use common regular expressions defined within it.



Removes a language and its aliases from the library. Used mostly internally.

  • languageName: a string with the name of the language being removed.


registerAliases(alias|aliases, {languageName})

Adds new language alias or aliases to the library for the specified language name defined under languageName key.

  • alias|aliases: a string or array with the name of alias being registered

  • languageName: the language name as specified by registerLanguage.


Returns the languages names list.



Looks up a language by name or alias.

Returns the language object if found, undefined otherwise.



Returns the full Highlight.js version as a string, ie: "11.0.1".



Enables safe mode. This is the default mode, providing the most reliable experience for production usage.



Enables debug/development mode.


This mode purposely makes Highlight.js more fragile! It should only be used for testing and local development (of languages or the library itself).

For example, if a new version suddenly had a serious bug (or breaking change) that affected only a single language:

  • In Safe Mode all other languages would continue to highlight just fine. The broken language would appear as a code block, but without any highlighting (as if it were plaintext).

  • In Debug Mode all highlighting would stop and a JavaScript error would be thrown.



Add a plugin to this instance of Highlight.js. See the plugin api for additional plugin information.



Remove the specified plugin from this instance. plugin must be exactly the same object that was passed to addPlugin.

Deprecated API


Deprecated since version 10.7: This will be removed entirely in v12.

highlight(languageName, code)

Please see the newer API shown above.


Deprecated since version 11.0: Please use highlightElement() instead.


Deprecated since version 10.6: Please use highlightAll() instead.


Deprecated since version 10.6: Please use highlightAll() instead.