Creating a new language definition

This section will explain the usual workflow of creating a new language definition.

As an example, we will create the language definition of the fictional Foo's Binary, Artistic Robots™ language or just Foo Bar for short.

1. Create a new file components/prism-foo-bar.js.

   In this example, we choose foo-bar as the id of the new language. The language id has to be unique and should work well with the language-xxxx CSS class name Prism uses to refer to language definitions. Your language id should ideally match the regular expression /^[a-z][a-z\d]*(?:-[a-z][a-z\d]*)*$/.

2. Edit components.json to register the new language by adding it to the languages object. (Please note that all language entries are sorted alphabetically by title.)
   Our new entry for this example will look like this:

   "foo-bar": {
   	"title": "Foo Bar",
   	"owner": "Your GitHub name"
   }

   If your language definition depends any other languages, you have to specify this here as well by adding a "require" property. E.g. "require": "clike", or "require" : ["markup", "css"]. For more information on dependencies read the declaring dependencies section.

   Note: Any changes made to components.json require a rebuild (see step 3).

3. Rebuild Prism by running npm run build.

   This will make your language available to the test page, or more precise: your local version of it. You can open your local test.html page in any browser, select your language, and see how your language definition highlights any code you input.

   Note: You have to reload the test page to apply changes made to prism-foo-bar.js but you don't have to rebuild Prism itself. However, if you change components.json (e.g. because you added a dependency) then these changes will not show up until you rebuild Prism.

4. Write the language definition.

   The above section already explains the makeup of language definitions.

5. Adding aliases.

   Aliases for are useful if your language is known under more than just one name or there are very common abbreviations for your language (e.g. JS for JavaScript). Keep in mind that aliases are very similar to language ids in that they also have to be unique (i.e. there cannot be an alias which is the same as another alias of language id) and work as CSS class names.

   In this example, we will register the alias foo for foo-bar because Foo Bar code is stored in .foo files.

   To add the alias, we add this line at the end of prism-foo-bar.js:

   Prism.languages.foo = Prism.languages['foo-bar'];

   Aliases also have to be registered in components.json by adding the alias property to the language entry. In this example, the updated entry will look like this:

   "foo-bar": {
   	"title": "Foo Bar",
   	"alias": "foo",
   	"owner": "Your GitHub name"
   }

   Note: alias can also be a string array if you need to register multiple aliases.

   Using aliasTitles, it's also possible to give aliases specific titles. In this example, this won't be necessary but a good example as to where this is useful is the markup language:

   "markup": {
   	"title": "Markup",
   	"alias": ["html", "xml", "svg", "mathml"],
   	"aliasTitles": {
   		"html": "HTML",
   		"xml": "XML",
   		"svg": "SVG",
   		"mathml": "MathML"
   	},
   	"option": "default"
   }

6. Add some tests.

   Create a folder tests/languages/foo-bar/. This is where your test files will live. The test format and how to run tests is described here.

   You should add a test for every major feature of your language. Test files should test the common case and certain edge cases (if any). Good examples are the tests of the JavaScript language.

   You can use this template for new .test files:

   The code to test.
   
   ----------------------------------------------------
   
   [ "JSON of the simplified token stream. We will add this later." ]
   
   ----------------------------------------------------
   
   Brief description.

   For every test file:

   1. Add the code to test and a brief description.

   2. Verify that your language definition correctly highlights the test code. This can be done using the test page.
      Note: Using the Show tokens options, you see the token stream your language definition created.

   3. Once you carefully checked that the test case is handled correctly (i.e. by using the test page), run the following command:

      npm run test:languages -- --language=foo-bar --pretty

      This command will check only your test files. The new test will fail because the specified JSON is incorrect but the error message of the failed test will also include the JSON of the simplified token stream Prism created. This is what we're after. Replace the current incorrect JSON with the output labeled Token Stream. (Please also adjust the indentation. We use tabs.)

   4. Carefully check that the token stream JSON you just inserted is what you expect.

   5. Re-run npm run test:languages -- --language=foo-bar --pretty to verify that the test passes.

7. Run npm test to check that all tests pass, not just your language tests.
   This will usually pass without problems. If you can't get all the tests to pass, skip this step.

8. Add an example page.

   Create a new file examples/prism-foo-bar.html. This will be the template containing the example markup. Just look at other examples to see how these files are structured.
   We don't have any rules as to what counts as an example, so a single Full example section where you present the highlighting of the major features of the language is enough.

9. Run npm run build again.

   Your language definition is now ready!

Dependencies

Languages and plugins can depend on each other, so Prism has its own dependency system to declare and resolve dependencies.

Declaring dependencies

You declare a dependency by adding a property to the entry of your language or plugin in the components.json file. The name of the property will be dependency kind and its value will be the component id of the dependee. If multiple languages or plugins are depended upon then you can also declare an array of component ids.

In the following example, we will use the require dependency kind to declare that a fictional language Foo depends on the JavaScript language and that another fictional language Bar depends on both JavaScript and CSS.

{
	"languages": {
		"javascript": { "title": "JavaScript" },
		"css": { "title": "CSS" },
		...,
		"foo": {
			"title": "Foo",
			"require": "javascript"
		},
		"bar": {
			"title": "Bar",
			"require": ["css", "javascript"]
		}
	}
}

Dependency kinds

There are 3 kinds of dependencies:

require

Prism will ensure that all dependees are loaded before the depender.
You are not allowed to modify the dependees unless they are also declared as modify.

This kind of dependency is most useful if you e.g. extend another language or dependee as an embedded language (e.g. like PHP is embedded in HTML).

optional

Prims will ensure that an optional dependee is loaded before the depender if the dependee is loaded. Unlike require dependencies which also guarantee that the dependees are loaded, optional dependencies only guarantee the order of loaded components.
You are not allowed to modify the dependees. If you need to modify the optional dependee, declare it as modify instead.

This kind of dependency is useful if you have embedded languages but you want to give the users a choice as to whether they want to include the embedded language. By using optional dependencies, users can better control the bundle size of Prism by only including the languages they need.
E.g. HTTP can highlight JSON and XML payloads but it doesn't force the user to include these languages.

modify

This is an optional dependency which also declares that the depender might modify the dependees.

This kind of dependency is useful if your language modifies another language (e.g. by adding tokens).
E.g. CSS Extras adds new tokens to the CSS language.

To summarize the properties of the different dependency kinds:

Note: You can declare a component as both require and modify

Resolving dependencies

We consider the dependencies of components an implementation detail, so they may change from release to release. Prism will usually resolve dependencies for you automatically. So you won't have to worry about dependency loading if you download a bundle or use the loadLanguages function in NodeJS, the AutoLoader, or our Babel plugin.

If you have to resolve dependencies yourself, use the getLoader function exported by dependencies.js. Example:

const getLoader = require('prismjs/dependencies');
const components = require('prismjs/components');

const componentsToLoad = ['markup', 'css', 'php'];
const loadedComponents = ['clike', 'javascript'];

const loader = getLoader(components, componentsToLoad, loadedComponents);
loader.load(id => {
	require(`prismjs/components/prism-${id}.min.js`);
});

For more details on the getLoader API, check out the inline documentation.