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A simple template-based web scraping library for node.js

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# graze

A simple template-based web scraping library for node.js

Web scraping is a process which can leave even the most hardy developer with an unshakable feeling of disgust.  Graze tries to make web scraping as undisgusting as possible, by letting you construct a template that just takes a URL in, and gives a well structured Javascript object out.

## Quickstart

It's easiest to understand how it all works by looking at an example (in Coffeescript, if you don't mind).

```coffee
graze = require 'graze'

template = graze.template {
    '#searchResult tr': 
        results: [
            'td:nth-child(2)':
                '.detName a':
                    title: graze.text()
                    link: graze.attr('href')
                '[alt="Magnet link"]':
                    magnet_link: graze.parent().attr('href')
                '.detDesc':
                    description: graze.text()
                    size: ($el) -> $el.text().match(/Size\s*([^,]*),/)?[1]
            'td:nth-child(3)':
                seeders: graze.text()
        ]
}

# Simple usage
template.scrape('http://thepiratebay.se/search/something%20illegal/').then (data) ->
    console.log data

# Advanced usage
template.scrape
  uri: 'https://securewebsite.com/user/transactions'
  auth:
    username: 'admin'
    password: 'itsasecret'
.then (data) ->
    console.log data
.catch ({error, response, body}) ->
    # Handle error

###
Output on success:

{
    "results": [ {
        "title": "Chairlift - Something",
        "link": "http://thepiratebay.se/torrent/9360343/Chairlift_-_Something",
        "magnet_link": "magnet:?xt=urn:btih:1e4dc0a30c6c413c947bd7df11bc8bd764c3babd",
        "description": "Uploaded 12-17 17:53, Size 39.79 MiB, ULed by Anonymous",
        "size": "39.79 MiB",
        "seeders": 1,
    }, {
        ...
    } ]
}
###
```

A template is just a Javascript Object, structured hierarchically in a way similar to the HTML you're trying to scrape.  The keys and values of the objects that make up this template have special meanings.  There are two kinds of meanings that keys can take on:

- **A CSS Selector**: This changes the scope of the template that follows.  At first the entire web page is within scope, but when a CSS selector is encountered as a key, the scope is refined to the elements that match the selector.  The value of this key **must** be a plain Javascript Object, representing a nested template.
- **A name**: This specifies the key that will be used in the scraped results Object.  You'll get different scraping behaviour depending on the type of its value:
    - **A graze extractor**: This defines how to extract information from the HTML.  They might look familiar if you've used jQuery.  Pretend that the `graze` module is a jQuery object containing the elements in scope.  Whatever chain of methods you call here will be repeated on the web page's in-scope elements, and the final result will appear in the output object under the above name.
    - **A function**: A function which takes in a jQuery object, and returns the desired information.  Use a function if a graze extractor doesn't quite cut it.  If you need to get fancy, you can have the function take in two arguments, like `($el, $)`, which gives you direct access to jQuery's `$`.
    - **An array**: This represents an iterator, which iterates over all the elements in scope and applies the template or extractor within to each element.  The actual array you define here in is only of length 1, and contains the template, graze extractor, or function which will be evaluated with each element.  The final result will be an array containing the information scraped from each iterated element.  You can also nest arrays within arrays to iterate over deep structures.
    - **None of the above**: If you pass in a string or a number for example, it will simply reappear in the scraped results.

Scraping a website is as simple as calling the `template.scrape` function above.  It takes the same first argument as the `request` function in the popular library [request](https://www.npmjs.org/package/request).  It returns a [q](https://www.npmjs.org/package/q) promise object, which helps to stop pyramids of death and makes error handling far more sane.

## Pro tips

### Nesting templates

You might find yourself in a situation where you'd like to group properties together within a parent object, to give something like:

```javascript
{
    ...
    "properties": {
        "size": "1.2GB",
        "upload_date": "11/11/2011"
    },
    ...
}
```

This can be achieved using the special `graze.nest(template)` function, which takes in a template and returns a custom function.  This function takes in the current page scope and processes it using the given template, returning that as its extracted value.  So to achieve the above, you might create a template like:

```coffee
graze.template {
    ...
    properties: graze.nest
        '.detDesc':
            size: ($el) -> $el.text().match(/Size\s*([^,]*),/)?[1]
            upload_date: ($el) -> $el.text().match(/Uploaded ([^,]*),/)?[1]
    ...
}
```

### Accessing the response object

Custom functions are called with the request's `response` object as their context, so you can access things like the URL of the page being scraped as `this.request.href`.

### Processing HTML directly

If you'd rather not have `graze` handle your web-page retrieval, you can manually run a template on an HTML string by calling `template.process(html, context)`, where `context` is the context you wish your custom functions to run within.

# Javascript example

For those of you who prefer decaf:

```javascript
var graze = require('graze');

var template = graze.template({
    '#searchResult tr': {
        results: [{
            'td:nth-child(2)': {
                '.detName a': {
                    title: graze.text(),
                    link: graze.attr('href'),
                },
                '[alt="Magnet link"]': {
                    magnet_link: graze.parent().attr('href'),
                },
                '.detDesc': {
                    description: graze.text(),
                    size: function($el) { match = $el.text().match(/Size\s*([^,]*),/); return match && match[1] }
                },
            },
            'td:nth-child(3)': {
                seeders: graze.text(),
            },
        }],
    },
});

template.scrape({
    uri: 'https://securewebsite.com/user/transactions',
    auth: {
        username: 'admin',
        password: 'itsasecret',
    },
}).then(function(data) {
    console.log(data)
}).fail(function(data) {
    console.error(data.error, data.response, data.body)
});
```

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