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# [NWSAPI](http://dperini.github.io/nwsapi/)
Fast CSS Selectors API Engine
   
NWSAPI is the development progress of [NWMATCHER](https://github.com/dperini/nwmatcher) aiming at [Selectors Level 4](https://www.w3.org/TR/selectors-4/) conformance. It has been completely reworked to be easily extended and maintained. It is a right-to-left selector parser and compiler written in pure Javascript with no external dependencies. It was initially thought as a cross browser library to improve event delegation and web page scraping in various frameworks but it has become a popular replacement of the native CSS selection and matching functionality in newer browsers and headless environments.
It uses [regular expressions](https://en.wikipedia.org/wiki/Regular_expression) to parse CSS selector strings and [metaprogramming](https://en.wikipedia.org/wiki/Metaprogramming) to transforms these selector strings into Javascript function resolvers. This process is executed only once for each selector string allowing memoization of the function resolvers and achieving unmatched performances.
## Installation
To include NWSAPI in a standard web page:
```html
<script type="text/javascript" src="nwsapi.js"></script>
```
To include NWSAPI in a standard web page and automatically replace the native QSA:
```html
<script type="text/javascript" src="nwsapi.js" onload="NW.Dom.install()"></script>
```
To use NWSAPI with Node.js:
```
$ npm install nwsapi
```
NWSAPI currently supports browsers (as a global, `NW.Dom`) and headless environments (as a CommonJS module).
## Supported Selectors
Here is a list of all the CSS2/CSS3/CSS4 [Supported selectors](https://github.com/dperini/nwsapi/wiki/CSS-supported-selectors).
## Features and Compliance
You can read more about NWSAPI [features and compliance](https://github.com/dperini/nwsapi/wiki/Features-and-compliance) on the wiki.
## API
### DOM Selection
#### `ancestor( selector, context, callback )`
Returns a reference to the nearest ancestor element matching `selector`, starting at `context`. Returns `null` if no element is found. If `callback` is provided, it is invoked for the matched element.
#### `first( selector, context, callback )`
Returns a reference to the first element matching `selector`, starting at `context`. Returns `null` if no element matches. If `callback` is provided, it is invoked for the matched element.
#### `match( selector, element, callback )`
Returns `true` if `element` matches `selector`, starting at `context`; returns `false` otherwise. If `callback` is provided, it is invoked for the matched element.
#### `select( selector, context, callback )`
Returns an array of all the elements matching `selector`, starting at `context`; returns empty `Array` otherwise. If `callback` is provided, it is invoked for each matching element.
### DOM Helpers
#### `byId( id, from )`
Returns a reference to the first element with ID `id`, optionally filtered to descendants of the element `from`.
#### `byTag( tag, from )`
Returns an array of elements having the specified tag name `tag`, optionally filtered to descendants of the element `from`.
#### `byClass( class, from )`
Returns an array of elements having the specified class name `class`, optionally filtered to descendants of the element `from`.
### Engine Configuration
#### `configure( options )`
The following is the list of currently available configuration options, their default values and descriptions, they are boolean flags that can be set to `true` or `false`:
* `IDS_DUPES`: true - true to allow using multiple elements having the same id, false to disallow
* `LIVECACHE`: true - true for caching both results and resolvers, false for caching only resolvers
* `MIXEDCASE`: true - true to match tag names case insensitive, false to match using case sensitive
* `LOGERRORS`: true - true to print errors and warnings to the console, false to mute both of them
### Examples on extending the basic functionalities
#### `configure( { <configuration-flag>: [ true | false ] } )`
Disable logging errors/warnings to console, disallow duplicate ids. Example:
```js
NW.Dom.configure( { LOGERRORS: false, IDS_DUPES: false } );
```
NOTE: NW.Dom.configure() without parameters return the current configuration.
#### `registerCombinator( symbol, resolver )`
Registers a new symbol and its matching resolver in the combinators table. Example:
```js
NW.Dom.registerCombinator( '^', 'e.parentElement' );
```
#### `registerOperator( symbol, resolver )`
Registers a new symbol and its matching resolver in the attribute operators table. Example:
```js
NW.Dom.registerOperator( '!=', { p1: '^', p2: '$', p3: 'false' } );
```
#### `registerSelector( name, rexp, func )`
Registers a new selector, the matching RE and the resolver function, in the selectors table. Example:
```js
NW.Dom.registerSelector('Controls', /^\:(control)(.*)/i,
(function(global) {
return function(match, source, mode, callback) {
var status = true;
source = 'if(/^(button|input|select|textarea)/i.test(e.nodeName)){' + source + '}';
return { 'source': source, 'status': status };
};
})(this));
```
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