# snapdragon [](https://www.npmjs.com/package/snapdragon) [](https://npmjs.org/package/snapdragon) [](https://travis-ci.org/jonschlinkert/snapdragon)
> Fast, pluggable and easy-to-use parser-renderer factory.
## Install
Install with [npm](https://www.npmjs.com/):
```sh
$ npm install --save snapdragon
```
Created by [jonschlinkert](https://github.com/jonschlinkert) and [doowb](https://github.com/doowb).
**Features**
* Bootstrap your own parser, get sourcemap support for free
* All parsing and compiling is handled by simple, reusable middleware functions
* Inspired by the parsers in [pug](http://jade-lang.com) and [css](https://github.com/reworkcss/css).
## History
### v0.5.0
**Breaking changes**
Substantial breaking changes were made in v0.5.0! Most of these changes are part of a larger refactor that will be finished in 0.6.0, including the introduction of a `Lexer` class.
* Renderer was renamed to `Compiler`
* the `.render` method was renamed to `.compile`
* Many other smaller changes. A more detailed overview will be provided in 0.6.0. If you don't have to time review code, I recommend you wait for the 0.6.0 release.
## Usage examples
```js
var Snapdragon = require('snapdragon');
var snapdragon = new Snapdragon();
```
**Parse**
```js
var ast = snapdragon.parser('some string', options)
// parser middleware that can be called by other middleware
.set('foo', function () {})
// parser middleware, runs immediately in the order defined
.use(bar())
.use(baz())
```
**Render**
```js
// pass the `ast` from the parse method
var res = snapdragon.compiler(ast)
// compiler middleware, called when the name of the middleware
// matches the `node.type` (defined in a parser middleware)
.set('bar', function () {})
.set('baz', function () {})
.compile()
```
See the [examples](./examples/).
## Getting started
**Parsers**
Parsers are middleware functions used for parsing a string into an ast node.
```js
var ast = snapdragon.parser(str, options)
.use(function() {
var pos = this.position();
var m = this.match(/^\./);
if (!m) return;
return pos({
// `type` specifies the compiler to use
type: 'dot',
val: m[0]
});
})
```
**AST node**
When the parser finds a match, `pos()` is called, pushing a token for that node onto the ast that looks something like:
```js
{ type: 'dot',
val: '.',
position:
{ start: { lineno: 1, column: 1 },
end: { lineno: 1, column: 2 } }}
```
**Renderers**
Renderers are _named_ middleware functions that visit over an array of ast nodes to compile a string.
```js
var res = snapdragon.compiler(ast)
.set('dot', function (node) {
console.log(node.val)
//=> '.'
return this.emit(node.val);
})
```
**Source maps**
If you want source map support, make sure to emit the position as well.
```js
var res = snapdragon.compiler(ast)
.set('dot', function (node) {
return this.emit(node.val, node.position);
})
```
## Docs
### Parser middleware
A parser middleware is a function that returns an abject called a `token`. This token is pushed onto the AST as a node.
**Example token**
```js
{ type: 'dot',
val: '.',
position:
{ start: { lineno: 1, column: 1 },
end: { lineno: 1, column: 2 } }}
```
**Example parser middleware**
Match a single `.` in a string:
1. Get the starting position by calling `this.position()`
2. pass a regex for matching a single dot to the `.match` method
3. if **no match** is found, return `undefined`
4. if a **match** is found, `pos()` is called, which returns a token with:
- `type`: the name of the [compiler] to use
- `val`: The actual value captured by the regex. In this case, a `.`. Note that you can capture and return whatever will be needed by the corresponding [compiler].
- The ending position: automatically calculated by adding the length of the first capture group to the starting position.
## Renderer middleware
Renderers are run when the name of the compiler middleware matches the `type` defined on an ast `node` (which is defined in a parser).
**Example**
Exercise: Parse a dot, then compile it as an escaped dot.
```js
var ast = snapdragon.parser('.')
.use(function () {
var pos = this.position();
var m = this.match(/^\./);
if (!m) return;
return pos({
// define the `type` of compiler to use
type: 'dot',
val: m[0]
})
})
var result = snapdragon.compiler(ast)
.set('dot', function (node) {
return this.emit('\\' + node.val);
})
.compile()
console.log(result.output);
//=> '\.'
```
## API
### [Parser](lib/parser.js#L19)
Create a new `Parser` with the given `input` and `options`.
**Params**
* `input` **{String}**
* `options` **{Object}**
### [.define](lib/parser.js#L103)
Define a non-enumberable property on the `Parser` instance.
**Example**
```js
parser.define('foo', 'bar');
```
**Params**
* `key` **{String}**: propery name
* `val` **{any}**: property value
* `returns` **{Object}**: Returns the Parser instance for chaining.
Set parser `name` with the given `fn`
**Params**
* `name` **{String}**
* `fn` **{Function}**
Get parser `name`
**Params**
* `name` **{String}**
Push a `token` onto the `type` stack.
**Params**
* `type` **{String}**
* `returns` **{Object}** `token`
Pop a token off of the `type` stack
**Params**
* `type` **{String}**
* `returns` **{Object}**: Returns a token
Return true if inside a `stack` node. Types are `braces`, `parens` or `brackets`.
**Params**
* `type` **{String}**
* `returns` **{Boolean}**
**Example**
```js
parser.isType(node, 'brace');
```
**Params**
* `node` **{Object}**
* `type` **{String}**
* `returns` **{Boolean}**
### [.define](lib/compiler.js#L71)
Define a non-enumberable property on the `Compiler` instance.
**Example**
```js
compiler.define('foo', 'bar');
```
**Params**
* `key` **{String}**: propery name
* `val` **{any}**: property value
* `returns` **{Object}**: Returns the Compiler instance for chaining.
## About
### Related projects
* [braces](https://www.npmjs.com/package/braces): Fastest brace expansion for node.js, with the most complete support for the Bash 4.3 braces… [more](https://github.com/jonschlinkert/braces) | [homepage](https://github.com/jonschlinkert/braces "Fastest brace expansion for node.js, with the most complete support for the Bash 4.3 braces specification.")
* [expand-brackets](https://www.npmjs.com/package/expand-brackets): Expand POSIX bracket expressions (character classes) in glob patterns. | [homepage](https://github.com/jonschlinkert/expand-brackets "Expand POSIX bracket expressions (character classes) in glob patterns.")
* [extglob](https://www.npmjs.com/package/extglob): Convert extended globs to regex-compatible strings. Add (almost) the expressive power of regular expressions to… [more](https://github.com/jonschlinkert/extglob) | [homepage](https://github.com/jonschlinkert/extglob "Convert extended globs to regex-compatible strings. Add (almost) the expressive power of regular expressions to glob patterns.")
* [micromatch](https://www.npmjs.com/package/micromatch): Glob matching for javascript/node.js. A drop-in replacement and faster alternative to minimatch and multimatch. | [homepage](https://github.com/jonschlinkert/micromatch "Glob matching for javascript/node.js. A drop-in replacement and faster alternative to minimatch and multimatch.")
### Contributing
Pull requests and stars are always welcome. For bugs and feature requests, [please create an issue](../../issues/new).
### Contributors
| **Commits** | **Contributor**<br/> |
| --- | --- |
| 106 | [jonschlinkert](https://github.com/jonschlinkert) |
| 2 | [doowb](https://github.com/doowb) |
### Building docs
_(This document was generated by [verb-generate-readme](https://github.com/verbose/verb-generate-readme) (a [verb](https://github.com/verbose/verb) generator), please don't edit the readme directly. Any changes to the readme must be made in [.verb.md](.verb.md).)_
To generate the readme and API documentation with [verb](https://github.com/verbose/verb):
```sh
$ npm install -g verb verb-generate-readme && verb
```
### Running tests
Install dev dependencies:
```sh
$ npm install -d && npm test
```
### Author
**Jon Schlinkert**
* [github/jonschlinkert](https://github.com/jonschlinkert)
* [twitter/jonschlinkert](http://twitter.com/jonschlinkert)
### License
Copyright © 2016, [Jon Schlinkert](https://github.com/jonschlinkert).
Released under the [MIT license](https://github.com/jonschlinkert/snapdragon/blob/master/LICENSE).
***
_This file was generated by [verb-generate-readme](https://github.com/verbose/verb-generate-readme), v0.1.31, on October 10, 2016._
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