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API

If you want to run Prettier programmatically, check this page out.

import * as prettier from "prettier";

prettier.format(source, options)

format is used to format text using Prettier. options.parser must be set according to the language you are formatting (see the list of available parsers). Alternatively, options.filepath can be specified for Prettier to infer the parser from the file extension. Other options may be provided to override the defaults.

await prettier.format("foo ( );", { semi: false, parser: "babel" });
// -> 'foo()\n'

prettier.check(source [, options])

check checks to see if the file has been formatted with Prettier given those options and returns a Promise<boolean>. This is similar to the --check or --list-different parameter in the CLI and is useful for running Prettier in CI scenarios.

prettier.formatWithCursor(source [, options])

formatWithCursor both formats the code, and translates a cursor position from unformatted code to formatted code. This is useful for editor integrations, to prevent the cursor from moving when code is formatted.

The cursorOffset option should be provided, to specify where the cursor is. This option cannot be used with rangeStart and rangeEnd.

await prettier.formatWithCursor(" 1", { cursorOffset: 2, parser: "babel" });
// -> { formatted: '1;\n', cursorOffset: 1 }

prettier.resolveConfig(filePath [, options])

resolveConfig can be used to resolve configuration for a given source file, passing its path as the first argument. The config search will start at the file path and continue to search up the directory (you can use process.cwd() to start searching from the current directory). Or you can pass directly the path of the config file as options.config if you don’t wish to search for it. A promise is returned which will resolve to:

  • An options object, providing a config file was found.
  • null, if no file was found.

The promise will be rejected if there was an error parsing the configuration file.

If options.useCache is false, all caching will be bypassed.

const text = await fs.readFile(filePath, "utf8");
const options = await prettier.resolveConfig(filePath);
const formatted = await prettier.format(text, options);

If options.editorconfig is true and an .editorconfig file is in your project, Prettier will parse it and convert its properties to the corresponding Prettier configuration. This configuration will be overridden by .prettierrc, etc. Currently, the following EditorConfig properties are supported:

  • end_of_line
  • indent_style
  • indent_size/tab_width
  • max_line_length

prettier.resolveConfigFile([filePath])

resolveConfigFile can be used to find the path of the Prettier configuration file that will be used when resolving the config (i.e. when calling resolveConfig). A promise is returned which will resolve to:

  • The path of the configuration file.
  • null, if no file was found.

The promise will be rejected if there was an error parsing the configuration file.

The search starts at process.cwd(), or at filePath if provided. Please see the cosmiconfig docs for details on how the resolving works.

const configFile = await prettier.resolveConfigFile(filePath);
// you got the path of the configuration file

prettier.clearConfigCache()

When Prettier loads configuration files and plugins, the file system structure is cached for performance. This function will clear the cache. Generally this is only needed for editor integrations that know that the file system has changed since the last format took place.

prettier.getFileInfo(filePath [, options])

getFileInfo can be used by editor extensions to decide if a particular file needs to be formatted. This method returns a promise, which resolves to an object with the following properties:

{
  ignored: boolean;
  inferredParser: string | null;
}

The promise will be rejected if the type of filePath is not string.

Setting options.ignorePath (string) and options.withNodeModules (boolean) influence the value of ignored (false by default).

If the given filePath is ignored, the inferredParser is always null.

Providing plugin paths in options.plugins (string[]) helps extract inferredParser for files that are not supported by Prettier core.

When setting options.resolveConfig (boolean, default false), Prettier will resolve the configuration for the given filePath. This is useful, for example, when the inferredParser might be overridden for a subset of files.

prettier.getSupportInfo()

Returns a promise which resolves to an object representing the options, parsers, languages and file types Prettier supports.

The support information looks like this:

{
  languages: Array<{
    name: string;
    parsers: string[];
    group?: string;
    tmScope?: string;
    aceMode?: string;
    codemirrorMode?: string;
    codemirrorMimeType?: string;
    aliases?: string[];
    extensions?: string[];
    filenames?: string[];
    linguistLanguageId?: number;
    vscodeLanguageIds?: string[];
  }>;
}

Custom Parser API (removed)

Removed in v3.0.0 (superseded by the Plugin API)

Before plugins were a thing, Prettier had a similar but more limited feature called custom parsers. It’s been removed in v3.0.0 as its functionality was a subset of what the Plugin API did. If you used it, please check the example below on how to migrate.

❌ Custom parser API (removed):

import { format } from "prettier";

format("lodash ( )", {
  parser(text, { babel }) {
    const ast = babel(text);
    ast.program.body[0].expression.callee.name = "_";
    return ast;
  },
});
// -> "_();\n"

✔️ Plugin API:

import { format } from "prettier";
import pluginBabel from "prettier/plugins/babel";

const myCustomPlugin = {
  parsers: {
    "my-custom-parser": {
      async parse(text) {
        const ast = await pluginBabel.parsers.babel.parse(text);
        ast.program.body[0].expression.callee.name = "_";
        return ast;
      },
      astFormat: "estree",
    },
  },
};

await format("lodash ( )", {
  parser: "my-custom-parser",
  plugins: [myCustomPlugin],
});
// -> "_();\n"

Note: Overall, doing codemods this way isn’t recommended. Prettier uses the location data of AST nodes for many things like preserving blank lines and attaching comments. When the AST is modified after the parsing, the location data often gets out of sync, which may lead to unpredictable results. Consider using jscodeshift if you need codemods.

As part of the removed Custom parser API, it was previously possible to pass a path to a module exporting a parse function via the --parser option. Use the --plugin CLI option or the plugins API option instead to load plugins.

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