Catharsis

A JavaScript parser for Google Closure Compiler and JSDoc type expressions.

Catharsis is designed to be:

• Accurate. Catharsis is based on a PEG.js grammar that's designed to handle any valid type expression. It uses a thorough test suite to verify the parser's accuracy.
• Fast. Parse results are cached, so the parser is invoked only when necessary.
• Flexible. Catharsis can convert a parse result back into a type expression, or into a description of the type expression. In addition, Catharsis can parse JSDoc-style type expressions.

Example

const catharsis = require('catharsis');

// Closure Compiler parsing
const type = '!Object';
let parsedType;
try {
  parsedType = catharsis.parse(type); // {"type":"NameExpression,"name":"Object","nullable":false}
} catch(e) {
  console.error('unable to parse %s: %s', type, e);
}

// JSDoc-style type expressions enabled
const jsdocType = 'string[]';  // Closure Compiler expects Array<string>
let parsedJsdocType;
try {
  parsedJsdocType = catharsis.parse(jsdocType, { jsdoc: true });
} catch (e) {
  console.error('unable to parse %s: %s', jsdocType, e);
}

// Converting parse results back to type expressions
catharsis.stringify(parsedType);                              // !Object
catharsis.stringify(parsedJsdocType);                         // string[]
catharsis.stringify(parsedJsdocType, {restringify: true});    // Array<string>

// Converting parse results to descriptions of the type expression
catharsis.describe(parsedType).simple;                        // non-null Object
catharsis.describe(parsedJsdocType).simple;                   // Array of string

See the test/specs directory for more examples of Catharsis' parse results.

Methods

parse(typeExpression, options)

Parse a type expression, and return the parse results. Throws an error if the type expression cannot be parsed.

When called without options, Catharsis attempts to parse type expressions in the same way as Closure Compiler. When the jsdoc option is enabled, Catharsis can also parse several kinds of type expressions that are permitted in JSDoc:

• The string function is treated as a function type with no parameters.
• If you append [] to a name expression (for example, string[]), it is interpreted as a type application with the expression Array (for example, Array<string>).
• Name expressions can contain the characters #, ~, :, and /.
• Name expressions can contain a suffix that is similar to a function signature (for example, MyClass(foo, bar)).
• Name expressions can contain a reserved word.
• Record types can use types other than name expressions for keys.

Parameters

• type: A string containing a Closure Compiler type expression.
• options: Options for parsing the type expression.
  • options.jsdoc: Specifies whether to enable parsing of JSDoc-style type expressions. Defaults to false.
  • options.useCache: Specifies whether to use the cache of parsed types. Defaults to true.

Returns

An object containing the parse results. See the test/specs directory for examples of the parse results for different type expressions.

The object also includes two non-enumerable properties:

• jsdoc: A boolean that indicates whether the type expression was parsed with JSDoc support enabled.
• typeExpression: A string that contains the type expression that was parsed.

stringify(parsedType, options)

Stringify parsedType, and return the type expression. If validation is enabled, throws an error if the stringified type expression cannot be parsed.

Parameters

• parsedType: An object containing a parsed Closure Compiler type expression.
• options: Options for stringifying the parse results.
  • options.cssClass: Synonym for options.linkClass. Deprecated in version 0.8.0; will be removed in a future version.
  • options.htmlSafe: Specifies whether to return an HTML-safe string that replaces left angle brackets (<) with the corresponding entity (<). Note: Characters in name expressions are not escaped.
  • options.linkClass: A CSS class to add to HTML links. Used only if options.links is provided. By default, no CSS class is added.
  • options.links: An object or map whose keys are name expressions and whose values are URIs. You can also provide a map-like object with a get() method. If a name expression matches a key in options.links, the name expression will be wrapped in an HTML <a> tag that links to the URI. If you also specify options.linkClass, the <a> tag includes a class attribute. Note: When using this option, parsed types are always restringified, and the resulting string is not cached.
  • options.restringify: Forces Catharsis to restringify the parsed type. If this option is not specified, and the parsed type object includes a typeExpression property, Catharsis returns the typeExpression property without modification when possible. Defaults to false.
  • options.useCache: Specifies whether to use the cache of stringified type expressions. Defaults to true.
  • options.validate: Specifies whether to validate the stringified parse results by attempting to parse them as a type expression. If the stringified results are not parsable with the default options, you must also provide the appropriate options to pass to the parse() method. Defaults to false.

Returns

A string containing the type expression.

describe(parsedType, options)

Convert a parsed type to a description of the type expression. This method is especially useful if your users are not familiar with the syntax for type expressions.

The describe() method returns the description in two formats:

• Simple format. A string that provides a complete description of the type expression.
• Extended format. An object that separates out some of the details about the outermost type expression, such as whether the type is optional, nullable, or repeatable.

For example, when you call describe('?function(new:MyObject, string)='), the method returns the following data:

{
  simple: 'optional nullable function(constructs MyObject, string)',
  extended: {
    description: 'function(string)',
    modifiers: {
      functionNew: 'Returns MyObject when called with new.',
      functionThis: '',
      optional: 'Optional.',
      nullable: 'May be null.',
      repeatable: ''
    },
    returns: ''
  }
}

Parameters

• parsedType: An object containing a parsed Closure Compiler type expression.
• options: Options for creating the description.
  • options.codeClass: A CSS class to add to the tag that is wrapped around type names. Used only if you specify options.codeTag. By default, no CSS class is added.
  • options.codeTag: The name of an HTML tag (for example, code) to wrap around type names. For example, if this option is set to code, the type expression Array<string> would have the simple description <code>Array</code> of <code>string</code>.
  • options.language: A string identifying the language in which to generate the description. The identifier should be an ISO 639-1 language code (for example, en). It can optionally be followed by a hyphen and an ISO 3166-1 alpha-2 country code (for example, en-US). If you use values other than en, you must provide translation resources in options.resources. Defaults to en.
  • options.linkClass: A CSS class to add to HTML links. Used only if options.links is provided. By default, no CSS class is added.
  • options.links: An object or map whose keys are name expressions and whose values are URIs. You can also provide a map-like object with a get() method. If a name expression matches a key in options.links, the name expression will be wrapped in an HTML <a> tag that links to the URI. If you also specify options.linkClass, the <a> tag includes a class attribute. Note: When you use this option, the description is not cached.
  • options.resources: An object that specifies how to describe type expressions for a given language. The object's property names should use the same format as options.language. Each property should contain an object in the same format as the translation resources in res/en.json. If you specify a value for options.resources.en, that value overrides the defaults in res/en.json.
  • options.useCache: Specifies whether to use the cache of descriptions. Defaults to true.

Returns

An object with the following properties:

• simple: A string that provides a complete description of the type expression.
• extended: An object containing details about the outermost type expression.
  • extended.description: A string that provides a basic description of the type expression, excluding the information contained in other properties.
  • extended.modifiers: Information about modifiers that apply to the type expression.
    • extended.modifiers.functionNew: A string that describes what a function returns when called with new. Returned only for function types.
    • extended.modifiers.functionThis: A string that describes what the keyword this refers to within a function. Returned only for function types.
    • extended.modifiers.nullable: A string that indicates whether the type is nullable or non-nullable.
    • extended.modifiers.optional: A string that indicates whether the type is optional.
    • extended.modifiers.repeatable: A string that indicates whether the type can be repeated.
  • extended.returns: A string that describes the function's return value. Returned only for function types.

Changelog

• 0.10.0 (December 2024):
  • The stringify() method no longer includes a dot separator for type applications. For example, an array of numbers is stringified as Array<number> rather than Array.<number>.
  • For the stringify() method, when options.htmlSafe is set to true, the < and > characters in type applications are escaped. Previously, only the < character was escaped.
  • For the describe() and stringify() methods, the options.links parameter now accepts a map-like object that has a get() method. The get() method must accept a key and return a value.
• 0.9.0 (June 2020):
  • For the describe() and stringify() methods, the options.links parameter now accepts either a map or an object.
  • Catharsis now requires Node.js 10 or later.
• 0.8.11 (July 2019): Updated dependencies.
• 0.8.10 (May 2019): Updated dependencies.
• 0.8.9 (July 2017): Type expressions that include an @ sign (for example, module:@prefix/mymodule~myCallback) are now supported.
• 0.8.8 (April 2016): Corrected the description of type applications other than arrays that contain a single type (for example, Promise.<string>).
• 0.8.7 (June 2015):
  • Record types that use numeric literals as property names (for example, {0: string}) are now parsed correctly.
  • Record types with a property that contains a function, with no space after the preceding colon (for example, {foo:function()}), are now parsed correctly.
  • Repeatable function parameters are no longer required to be enclosed in brackets, regardless of whether JSDoc-style type expressions are enabled. In addition, the brackets are omitted when stringifying a parsed type expression.
• 0.8.6 (December 2014): Improved the description of the unknown type.
• 0.8.5 (December 2014): Added support for postfix nullable/non-nullable operators combined with the optional operator (for example, foo?=).
• 0.8.4 (December 2014): JSDoc-style nested arrays (for example, number[][]) are now parsed correctly when JSDoc-style type expressions are enabled.
• 0.8.3 (October 2014):
  • Type applications are no longer required to include a period (.) as a separator, regardless of whether JSDoc-style type expressions are enabled.
  • Type unions that are not enclosed in parentheses can now include the repeatable (...) modifier when JSDoc-style type expressions are enabled.
  • Name expressions may now be enclosed in single or double quotation marks when JSDoc-style type expressions are enabled.
• 0.8.2 (June 2014): Fixed a compatibility issue with the JSDoc fork of Mozilla Rhino.
• 0.8.1 (June 2014): Added support for type unions that are not enclosed in parentheses, and that contain nullable or non-nullable modifiers (for example, !string|!number).
• 0.8.0 (May 2014):
  • Added a describe() method, which converts a parsed type to a description of the type.
  • Added a linkClass option to the stringify() method, and deprecated the existing cssClass option. The cssClass option will be removed in a future release.
  • Clarified and corrected several sections in the README.
• 0.7.1 (April 2014): In record types, property names that begin with a keyword (for example, undefinedHTML) are now parsed correctly when JSDoc-style type expressions are enabled.
• 0.7.0 (October 2013):
  • Repeatable type expressions other than name expressions (for example, ...function()) are now parsed and stringified correctly.
  • Type expressions that are both repeatable and either nullable or non-nullable (for example, ...!number) are now parsed and stringified correctly.
  • Name expressions are now parsed correctly when they match a property name in an object instance (for example, constructor).
• 0.6.0 (September 2013): Added support for the type expression function[] when JSDoc-style type expressions are enabled.
• 0.5.6 (April 2013):
  • For consistency with Closure Compiler, parentheses are no longer required around type unions, regardless of whether JSDoc-style type expressions are enabled.
  • For consistency with Closure Compiler, you can now use postfix notation for the ? (nullable) and ! (non-nullable) modifiers. For example, ?string and string? are now treated as equivalent.
  • String literals and numeric literals are now allowed as property names within name expressions. For example, the name expression Foo."bar" is now parsed correctly.
• 0.5.5 (April 2013): Corrected a parsing issue with name expressions that end with a value enclosed in parentheses.
• 0.5.4 (April 2013):
  • Repeatable literals (for example, ...*) are now parsed correctly.
  • When JSDoc-style type expressions are enabled, a name expression can now contain a value enclosed in parentheses at the end of the name expression (for example, MyClass(2)).
• 0.5.3 (March 2013): The parse() method now correctly parses name expressions that contain hyphens.
• 0.5.2 (March 2013): The parse() method now correctly parses function types when JSDoc-style type expressions are enabled.
• 0.5.1 (March 2013): Newlines and extra spaces are now removed from type expressions before they are parsed.
• 0.5.0 (March 2013):
  • The parse() method's lenient option has been renamed to jsdoc. Note: This change is not backwards-compatible with previous versions.
  • The stringify() method now accepts cssClass and links options, which you can use to add HTML links to a type expression.
• 0.4.3 (March 2013):
  • The stringify() method no longer caches HTML-safe type expressions as if they were normal type expressions.
  • The stringify() method's options parameter may now include an options.restringify property, and the behavior of the options.useCache property has changed.
• 0.4.2 (March 2013):
  • When lenient parsing is enabled, name expressions can now contain the characters : and /.
  • When lenient parsing is enabled, a name expression followed by [] (for example, string[]) will be interpreted as a type application with the expression Array (for example, Array.<string>).
• 0.4.1 (March 2013):
  • The parse() and stringify() methods now honor all of the specified options.
  • When lenient parsing is enabled, name expressions can now contain a reserved word.
• 0.4.0 (March 2013):
  • Catharsis now supports a lenient parsing option that can parse several kinds of malformed type expressions. See the documentation for details.
  • The objects containing parse results are now frozen.
  • The objects containing parse results now have two non-enumerable properties:
    • lenient: A boolean indicating whether the type expression was parsed in lenient mode.
    • typeExpression: A string containing the original type expression.
  • The stringify() method now honors the useCache option. If a parsed type includes a typeExpression property, and useCache is not set to false, the stringified type will be identical to the original type expression.
• 0.3.1 (March 2013): Type expressions that begin with a reserved word, such as integer, are now parsed correctly.
• 0.3.0 (March 2013):
  • The parse() and stringify() methods are now synchronous, and the parseSync() and stringifySync() methods have been removed. Note: This change is not backwards-compatible with previous versions.
  • The parse results now use a significantly different format from previous versions. The new format is more expressive and is similar, but not identical, to the format used by the doctrine parser. Note: This change is not backwards-compatible with previous versions.
  • Name expressions that contain a reserved word now include a reservedWord: true property.
  • Union types that are optional or nullable, or that can be repeated, are now parsed and stringified correctly.
  • Optional function types and record types are now parsed and stringified correctly.
  • Function types now longer include new or this properties unless the properties are defined in the type expression. In addition, the new and this properties can now use any type expression.
  • In record types, the key for a field type can now use any type expression.
  • Standalone single-character literals, such as ALL (*), are now parsed and stringified correctly.
  • null and undefined literals with additional properties, such as repeatable, are now stringified correctly.
• 0.2.0 (November 2012):
  • Added stringify() and stringifySync() methods, which convert a parsed type to a type expression.
  • Simplified the parse results for function signatures. Note: This change is not backwards-compatible with previous versions.
  • Corrected minor errors in README.md.
• 0.1.1 (November 2012): Added opts argument to parse() and parseSync() methods. Note: The change to parse() is not backwards-compatible with previous versions.
• 0.1.0 (November 2012): Initial release.

License

MIT license.