https://github.com/here-be/snapdragon-lexer
Converts a string into an array of tokens, with useful methods for looking ahead and behind, capturing, matching, et cetera.
https://github.com/here-be/snapdragon-lexer
doowb javascript jonschlinkert lexer node nodejs parse snapdragon token tokenizer
Last synced: 11 days ago
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Converts a string into an array of tokens, with useful methods for looking ahead and behind, capturing, matching, et cetera.
- Host: GitHub
- URL: https://github.com/here-be/snapdragon-lexer
- Owner: here-be
- License: mit
- Created: 2017-12-01T03:07:04.000Z (almost 8 years ago)
- Default Branch: master
- Last Pushed: 2018-11-19T16:28:16.000Z (almost 7 years ago)
- Last Synced: 2025-03-25T21:06:58.999Z (7 months ago)
- Topics: doowb, javascript, jonschlinkert, lexer, node, nodejs, parse, snapdragon, token, tokenizer
- Language: JavaScript
- Homepage: https://github.com/here-be
- Size: 71.3 KB
- Stars: 21
- Watchers: 3
- Forks: 5
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- Contributing: .github/contributing.md
- License: LICENSE
Awesome Lists containing this project
README
# snapdragon-lexer [](https://www.npmjs.com/package/snapdragon-lexer) [](https://npmjs.org/package/snapdragon-lexer) [](https://npmjs.org/package/snapdragon-lexer) [](https://travis-ci.org/here-be/snapdragon-lexer)
> Converts a string into an array of tokens, with useful methods for looking ahead and behind, capturing, matching, et cetera.
Please consider following this project's author, [Jon Schlinkert](https://github.com/jonschlinkert), and consider starring the project to show your :heart: and support.
## Table of Contents
Details
- [Install](#install)
- [Breaking changes in v2.0!](#breaking-changes-in-v20)
- [Usage](#usage)
- [API](#api)
* [.set](#set)
* [.get](#get)
- [Properties](#properties)
* [lexer.isLexer](#lexerislexer)
* [lexer.input](#lexerinput)
* [lexer.string](#lexerstring)
* [lexer.consumed](#lexerconsumed)
* [lexer.tokens](#lexertokens)
* [lexer.stash](#lexerstash)
* [lexer.stack](#lexerstack)
* [lexer.queue](#lexerqueue)
* [lexer.loc](#lexerloc)
- [Options](#options)
* [options.source](#optionssource)
* [options.mode](#optionsmode)
* [options.value](#optionsvalue)
- [Tokens](#tokens)
- [Plugins](#plugins)
* [Plugin Conventions](#plugin-conventions)
- [About](#about)
## Install
Install with [npm](https://www.npmjs.com/):
```sh
$ npm install --save snapdragon-lexer
```
## Breaking changes in v2.0!
Please see the [changelog](CHANGELOG.md) for details!
## Usage
```js
const Lexer = require('snapdragon-lexer');
const lexer = new Lexer();
lexer.capture('slash', /^\//);
lexer.capture('text', /^\w+/);
lexer.capture('star', /^\*/);
console.log(lexer.tokenize('foo/*'));
```
## API
### [Lexer](index.js#L23)
Create a new `Lexer` with the given `options`.
**Params**
* `input` **{string|Object}**: (optional) Input string or options. You can also set input directly on `lexer.input` after initializing.
* `options` **{object}**
**Example**
```js
const Lexer = require('snapdragon-lexer');
const lexer = new Lexer('foo/bar');
```
### [.bos](index.js#L53)
Returns true if we are still at the beginning-of-string, and
no part of the string has been consumed.
* `returns` **{boolean}**
### [.eos](index.js#L65)
Returns true if `lexer.string` and `lexer.queue` are empty.
* `returns` **{boolean}**
### [.set](index.js#L83)
Register a handler function.
**Params**
* `type` **{string}**
* `fn` **{function}**: The handler function to register.
**Example**
```js
lexer.set('star', function() {
// do parser, lexer, or compiler stuff
});
```
### [.get](index.js#L119)
Get a registered handler function.
**Params**
* `type` **{string}**
* `fn` **{function}**: The handler function to register.
**Example**
```js
lexer.set('star', function() {
// do lexer stuff
});
const star = lexer.get('star');
```
### [.has](index.js#L138)
Returns true if the lexer has a registered handler of the given `type`.
**Params**
* **{string}**: type
* `returns` **{boolean}**
**Example**
```js
lexer.set('star', function() {});
console.log(lexer.has('star')); // true
```
### [.token](index.js#L159)
Create a new [Token](https://github.com/here-be/snapdragon-token) with the given `type` and `value`.
**Params**
* `type` **{string|Object}**: (required) The type of token to create
* `value` **{string}**: (optional) The captured string
* `match` **{array}**: (optional) Match results from `String.match()` or `RegExp.exec()`
* `returns` **{Object}**: Returns an instance of [snapdragon-token](https://github.com/here-be/snapdragon-token)
**Events**
* `emits`: token
**Example**
```js
console.log(lexer.token({type: 'star', value: '*'}));
console.log(lexer.token('star', '*'));
console.log(lexer.token('star'));
```
### [.isToken](index.js#L179)
Returns true if the given value is a [snapdragon-token](https://github.com/here-be/snapdragon-token) instance.
**Params**
* `token` **{object}**
* `returns` **{boolean}**
**Example**
```js
const Token = require('snapdragon-token');
lexer.isToken({}); // false
lexer.isToken(new Token({type: 'star', value: '*'})); // true
```
### [.consume](index.js#L198)
Consume the given length from `lexer.string`. The consumed value is used to update `lexer.state.consumed`, as well as the current position.
**Params**
* `len` **{number}**
* `value` **{string}**: Optionally pass the value being consumed.
* `returns` **{String}**: Returns the consumed value
**Example**
```js
lexer.consume(1);
lexer.consume(1, '*');
```
Returns a function for updating a token with lexer
location information.
* `returns` **{function}**
### [.match](index.js#L255)
Use the given `regex` to match a substring from `lexer.string`. Also validates the regex to ensure that it starts with `^` since matching should always be against the beginning of the string, and throws if the regex matches an empty string, which can cause catastrophic backtracking.
**Params**
* `regex` **{regExp}**: (required)
* `returns` **{Array|null}**: Returns the match array from `RegExp.exec` or null.
**Example**
```js
const lexer = new Lexer('foo/bar');
const match = lexer.match(/^\w+/);
console.log(match);
//=> [ 'foo', index: 0, input: 'foo/bar' ]
```
### [.scan](index.js#L301)
Scan for a matching substring by calling [.match()](#match) with the given `regex`. If a match is found, 1) a token of the specified `type` is created, 2) `match[0]` is used as `token.value`, and 3) the length of `match[0]` is sliced from `lexer.string` (by calling [.consume()](#consume)).
**Params**
* `type` **{string}**
* `regex` **{regExp}**
* `returns` **{Object}**: Returns a token if a match is found, otherwise undefined.
**Events**
* `emits`: scan
**Example**
```js
lexer.string = '/foo/';
console.log(lexer.scan(/^\//, 'slash'));
//=> Token { type: 'slash', value: '/' }
console.log(lexer.scan(/^\w+/, 'text'));
//=> Token { type: 'text', value: 'foo' }
console.log(lexer.scan(/^\//, 'slash'));
//=> Token { type: 'slash', value: '/' }
```
### [.capture](index.js#L338)
Capture a token of the specified `type` using the provide `regex` for scanning and matching substrings. Automatically registers a handler when a function is passed as the last argument.
**Params**
* `type` **{string}**: (required) The type of token being captured.
* `regex` **{regExp}**: (required) The regex for matching substrings.
* `fn` **{function}**: (optional) If supplied, the function will be called on the token before pushing it onto `lexer.tokens`.
* `returns` **{Object}**
**Example**
```js
lexer.capture('text', /^\w+/);
lexer.capture('text', /^\w+/, token => {
if (token.value === 'foo') {
// do stuff
}
return token;
});
```
### [.handle](index.js#L370)
Calls handler `type` on `lexer.string`.
**Params**
* `type` **{string}**: The handler type to call on `lexer.string`
* `returns` **{Object}**: Returns a token of the given `type` or undefined.
**Events**
* `emits`: handle
**Example**
```js
const lexer = new Lexer('/a/b');
lexer.capture('slash', /^\//);
lexer.capture('text', /^\w+/);
console.log(lexer.handle('text'));
//=> undefined
console.log(lexer.handle('slash'));
//=> { type: 'slash', value: '/' }
console.log(lexer.handle('text'));
//=> { type: 'text', value: 'a' }
```
### [.advance](index.js#L393)
Get the next token by iterating over `lexer.handlers` and calling each handler on `lexer.string` until a handler returns a token. If no handlers return a token, an error is thrown with the substring that couldn't be lexed.
* `returns` **{Object}**: Returns the first token returned by a handler, or the first character in the remaining string if `options.mode` is set to `character`.
**Example**
```js
const token = lexer.advance();
```
### [.lex](index.js#L429)
Tokenizes a string and returns an array of tokens.
**Params**
* `input` **{string}**: The string to lex.
* `returns` **{Array}**: Returns an array of tokens.
**Example**
```js
let lexer = new Lexer({ handlers: otherLexer.handlers })
lexer.capture('slash', /^\//);
lexer.capture('text', /^\w+/);
const tokens = lexer.lex('a/b/c');
console.log(tokens);
// Results in:
// [ Token { type: 'text', value: 'a' },
// Token { type: 'slash', value: '/' },
// Token { type: 'text', value: 'b' },
// Token { type: 'slash', value: '/' },
// Token { type: 'text', value: 'c' } ]
```
### [.enqueue](index.js#L454)
Push a token onto the `lexer.queue` array.
**Params**
* `token` **{object}**
* `returns` **{Object}**: Returns the given token with updated `token.index`.
**Example**
```js
console.log(lexer.queue.length); // 0
lexer.enqueue(new Token('star', '*'));
console.log(lexer.queue.length); // 1
```
### [.dequeue](index.js#L472)
Shift a token from `lexer.queue`.
* `returns` **{Object}**: Returns the given token with updated `token.index`.
**Example**
```js
console.log(lexer.queue.length); // 1
lexer.dequeue();
console.log(lexer.queue.length); // 0
```
### [.lookbehind](index.js#L488)
Lookbehind `n` tokens.
**Params**
* `n` **{number}**
* `returns` **{Object}**
**Example**
```js
const token = lexer.lookbehind(2);
```
### [.prev](index.js#L504)
Get the previously lexed token.
* `returns` **{Object|undefined}**: Returns a token or undefined.
**Example**
```js
const token = lexer.prev();
```
### [.lookahead](index.js#L522)
Lookahead `n` tokens and return the last token. Pushes any intermediate tokens onto `lexer.tokens.` To lookahead a single token, use [.peek()](#peek).
**Params**
* `n` **{number}**
* `returns` **{Object}**
**Example**
```js
const token = lexer.lookahead(2);
```
### [.peek](index.js#L540)
Lookahead a single token.
* `returns` **{Object}**: Returns a token.
**Example**
```js
const token = lexer.peek();
```
### [.next](index.js#L555)
Get the next token, either from the `queue` or by [advancing](#advance).
* `returns` **{Object|String}**: Returns a token, or (when `options.mode` is set to `character`) either gets the next character from `lexer.queue`, or consumes the next charcter in the string.
**Example**
```js
const token = lexer.next();
```
### [.skip](index.js#L571)
Skip `n` tokens or characters in the string. Skipped values are not enqueued.
**Params**
* `n` **{number}**
* `returns` **{Object}**: returns an array of skipped tokens.
**Example**
```js
const token = lexer.skip(1);
```
### [.skipWhile](index.js#L588)
Skip tokens while the given `fn` returns true.
**Params**
* `fn` **{function}**: Return true if a token should be skipped.
* `returns` **{Array}**: Returns an array if skipped tokens.
**Example**
```js
lexer.skipWhile(tok => tok.type !== 'space');
```
### [.skipType](index.js#L606)
Skip the given token `types`.
**Params**
* `types` **{string|Array}**: One or more token types to skip.
* `returns` **{Array}**: Returns an array if skipped tokens.
**Example**
```js
lexer.skipWhile(tok => tok.type !== 'space');
```
### [.skipType](index.js#L623)
Skip the given token `types`.
**Params**
* `types` **{string|Array}**: One or more token types to skip.
* `returns` **{Array}**: Returns an array if skipped tokens
**Example**
```js
lexer.skipType('space');
lexer.skipType(['newline', 'space']);
```
### [.push](index.js#L645)
Pushes the given `token` onto `lexer.tokens` and calls [.append()](#append) to push `token.value` onto `lexer.stash`. Disable pushing onto the stash by setting `lexer.options.append` or `token.append` to `false`.
**Params**
* `token` **{object|String}**
* `returns` **{Object}**: Returns the given `token`.
**Events**
* `emits`: push
**Example**
```js
console.log(lexer.tokens.length); // 0
lexer.push(new Token('star', '*'));
console.log(lexer.tokens.length); // 1
console.log(lexer.stash) // ['*']
```
### [.append](index.js#L686)
Append a string to the last element on `lexer.stash`, or push the string onto the stash if no elements exist.
**Params**
* `value` **{String}**
* `returns` **{String}**: Returns the last value in the array.
**Example**
```js
const stack = new Stack();
stack.push('a');
stack.push('b');
stack.push('c');
stack.append('_foo');
stack.append('_bar');
console.log(stack);
//=> Stack ['a', 'b', 'c_foo_bar']
```
### [.isInside](index.js#L712)
Returns true if a token with the given `type` is on the stack.
**Params**
* `type` **{string}**: The type to check for.
* `returns` **{boolean}**
**Example**
```js
if (lexer.isInside('bracket') || lexer.isInside('brace')) {
// do stuff
}
```
### [.error](index.js#L733)
Throw a formatted error message with details including the cursor position.
**Params**
* `msg` **{string}**: Message to use in the Error.
* `node` **{object}**
* `returns` **{undefined}**
**Example**
```js
lexer.set('foo', function(tok) {
if (tok.value !== 'foo') {
throw this.state.error('expected token.value to be "foo"', tok);
}
});
```
### [.use](index.js#L774)
Call a plugin function on the lexer instance.
**Params**
* `fn` **{function}**
* `returns` **{object}**: Returns the lexer instance.
**Example**
```js
lexer.use(function(lexer) {
// do stuff to lexer
});
```
### [Lexer#isLexer](index.js#L796)
Static method that returns true if the given value is an instance of `snapdragon-lexer`.
**Params**
* `lexer` **{object}**
* `returns` **{Boolean}**
**Example**
```js
const Lexer = require('snapdragon-lexer');
const lexer = new Lexer();
console.log(Lexer.isLexer(lexer)); //=> true
console.log(Lexer.isLexer({})); //=> false
```
### [Lexer#isToken](index.js#L817)
Static method that returns true if the given value is an instance of `snapdragon-token`. This is a proxy to `Token#isToken`.
**Params**
* `lexer` **{object}**
* `returns` **{Boolean}**
**Example**
```js
const Token = require('snapdragon-token');
const Lexer = require('snapdragon-lexer');
console.log(Lexer.isToken(new Token({type: 'foo'}))); //=> true
console.log(Lexer.isToken({})); //=> false
```
### [Lexer#State](index.js#L828)
The State class, exposed as a static property.
### [Lexer#Token](index.js#L839)
The Token class, exposed as a static property.
### .set
Register a handler function.
**Params**
* `type` **{String}**
* `fn` **{Function}**: The handler function to register.
**Example**
```js
lexer.set('star', function(token) {
// do parser, lexer, or compiler stuff
});
```
As an alternative to `.set`, the [.capture](#capture) method will automatically register a handler when a function is passed as the last argument.
### .get
Get a registered handler function.
**Params**
* `type` **{String}**
* `fn` **{Function}**: The handler function to register.
**Example**
```js
lexer.set('star', function() {
// do parser, lexer, or compiler stuff
});
const star = handlers.get('star');
```
## Properties
### lexer.isLexer
Type: **{boolean}**
Default: `true` (contant)
This property is defined as a convenience, to make it easy for plugins to check for an instance of Lexer.
### lexer.input
Type: **{string}**
Default: `''`
The unmodified source string provided by the user.
### lexer.string
Type: **{string}**
Default: `''`
The source string minus the part of the string that has already been [consumed](#consume).
### lexer.consumed
Type: **{string}**
Default: `''`
The part of the source string that has been consumed.
### lexer.tokens
Type: **{array}**
Default: `[]
Array of lexed tokens.
### lexer.stash
Type: **{array}**
Default: `['']` (instance of [snapdragon-stack](https://github.com/here-be/snapdragon-stack))
Array of captured strings. Similar to the [lexer.tokens](#lexertokens) array, but stores strings instead of token objects.
### lexer.stack
Type: **{array}**
Default: `[]
LIFO (last in, first out) array. A token is pushed onto the stack when an "opening" character or character sequence needs to be tracked. When the (matching) "closing" character or character sequence is encountered, the (opening) token is popped off of the stack.
The stack is not used by any lexer methods, it's reserved for the user. Stacks are necessary for creating Abstract Syntax Trees (ASTs), but if you require this functionality it would be better to use a parser such as [snapdragon-parser][snapdragon-parser], with methods and other conveniences for creating an AST.
### lexer.queue
Type: **{array}**
Default: `[]
FIFO (first in, first out) array, for temporarily storing tokens that are created when [.lookahead()](#lookahead) is called (or a method that calls `.lookhead()`, such as [.peek()](#peek)).
Tokens are [dequeued](#dequeue) when [.next()](#next) is called.
### lexer.loc
Type: **{Object}**
Default: `{ index: 0, column: 0, line: 1 }`
The updated source string location with the following properties.
* `index` - 0-index
* `column` - 0-index
* `line` - 1-index
The following plugins are available for automatically updating tokens with the location:
* [snapdragon-location](https://github.com/here-be/snapdragon-location)
* [snapdragon-position](https://github.com/here-be/snapdragon-position)
## Options
### options.source
Type: **{string}**
Default: `undefined`
The source of the input string. This is typically a filename or file path, but can also be `'string'` if a string or buffer is provided directly.
If `lexer.input` is undefined, and `options.source` is a string, the lexer will attempt to set `lexer.input` by calling `fs.readFileSync()` on the value provided on `options.source`.
### options.mode
Type: **{string}**
Default: `undefined`
If `options.mode` is `character`, instead of calling handlers (which match using regex) the [.advance()](advance) method will [consume](#consume) and return one character at a time.
### options.value
Type: **{string}**
Default: `undefined`
Specify the token property to use when the [.push](#push) method pushes a value onto [lexer.stash](#lexerstash). The logic works something like this:
```js
lexer.append(token[lexer.options.value || 'value']);
```
## Tokens
See the [snapdragon-token](https://github.com/here-be/snapdragon-token) documentation for more details.
## Plugins
Plugins are registered with the `lexer.use()` method and use the following conventions.
### Plugin Conventions
Plugins are functions that take an instance of snapdragon-lexer.
However, it's recommended that you always wrap your plugin function in another function that takes an options object. This allow users to pass options when using the plugin. _Even if your plugin doesn't take options, it's a best practice for users to always be able to use the same signature_.
**Example**
```js
function plugin(options) {
return function(lexer) {
// do stuff
};
}
lexer.use(plugin());
```
## About
Contributing
Pull requests and stars are always welcome. For bugs and feature requests, [please create an issue](../../issues/new).
Please read the [contributing guide](.github/contributing.md) for advice on opening issues, pull requests, and coding standards.
Running Tests
Running and reviewing unit tests is a great way to get familiarized with a library and its API. You can install dependencies and run tests with the following command:
```sh
$ npm install && npm test
```
Building docs
_(This project's readme.md is generated by [verb](https://github.com/verbose/verb-generate-readme), please don't edit the readme directly. Any changes to the readme must be made in the [.verb.md](.verb.md) readme template.)_
To generate the readme, run the following command:
```sh
$ npm install -g verbose/verb#dev verb-generate-readme && verb
```
### Related projects
You might also be interested in these projects:
* [snapdragon-scanner](https://www.npmjs.com/package/snapdragon-scanner): Easily scan a string with an object of regex patterns to produce an array of… [more](https://github.com/here-be/snapdragon-scanner) | [homepage](https://github.com/here-be/snapdragon-scanner "Easily scan a string with an object of regex patterns to produce an array of tokens. ~100 sloc.")
### Author
**Jon Schlinkert**
* [GitHub Profile](https://github.com/jonschlinkert)
* [Twitter Profile](https://twitter.com/jonschlinkert)
* [LinkedIn Profile](https://linkedin.com/in/jonschlinkert)
### License
Copyright © 2018, [Jon Schlinkert](https://github.com/jonschlinkert).
Released under the [MIT License](LICENSE).
***
_This file was generated by [verb-generate-readme](https://github.com/verbose/verb-generate-readme), v0.8.0, on November 19, 2018._