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Scraping
Node.io includes a robust framework for scraping data from the web. The primary methods for scraping data are get
and getHtml
, although there are methods for making any type of request, modifying headers, etc. See the API for a full list of methods.
Note that var nodeio = require('node.io');
is omitted in each example.
Example 1: Save a web page to disk
The following script is equivalent to
$ curl "http://www.google.com/" > google.html
save.js
exports.job = new nodeio.Job({
input: false,
run: function () {
var self = this, url = this.options.args[0];
this.get(url, function(err, data) {
if (err) {
self.exit(err)
} else {
self.emit(data);
}
}
}
save.coffee
class SavePage extends nodeio.JobClass
input: false
run: () ->
url = @options.args[0]
@get url, (err, data) =>
if err? then @exit err else @emit data
To save a page to disk, run
$ node.io -s save "http://www.google.com/" > google.html
Example 2: Get the number of Google results for a list of keywords
To use node.io effectively, try and encapsulate common scraping code in run()
so that the resulting job is as generic and versatile as possible. Each thread should contain only one request where possible.
keywords.js
var options = {timeout: 10};
exports.job = new nodeio.Job(options, {
input: ['hello', 'foobar','weather'],
run: function (keyword) {
var self = this, results;
this.getHtml('http://www.google.com/search?q=' + encodeURIComponent(keyword), function (err, $) {
results = $('#resultStats').text.toLowerCase();
self.emit(keyword + ' has ' + results);
});
}
});
Note: you could also comment out input: ['hello', 'foobar','weather'],
and specify a list of keywords through the web interface or at the command line, e.g.
$ node.io keywords < list_of_words.js
Example 3: Scraping a page using CSS selector / traversal methods
When using getHtml(url, callback)
, the second argument of callback is $
, an object similar to jQuery's.
reddit.js - scrape the front page stories from reddit.com
var methods = {
input: false,
run: function() {
var self = this;
this.getHtml('http://www.reddit.com/', function(err, $) {
//Handle any request / parsing errors
if (err) self.exit(err);
var titles = [], scores = [], output = [];
//Select all titles on the page
$('a.title').each(function(a) {
titles.push(a.text);
});
//Select all scores on the page
$('div.score.unvoted').each(function(div) {
scores.push(div.rawtext); //rawtext doesn't decode entities or trim the text
});
//Mismatch? page probably didn't load properly
if (scores.length != titles.length) {
self.exit('Title / score mismatch');
}
for (var i = 0, len = scores.length; i < len; i++) {
//Ignore upcoming stories
if (scores[i] == '•') continue;
//Check the data is ok
self.assert(scores[i]).isInt();
//Output = [score] title
output.push('['+scores[i]+'] '+titles[i]);
}
self.emit(output);
});
}
}
exports.job = new Job({timeout:10}, methods);
reddit.coffee
titles = []
scores = []
output = []
class Reddit extends nodeio.JobClass
input: false
run: ->
@getHtml 'http://www.reddit.com/', (err, $, data) =>
@exit err if err?
$('a.title').each (a) -> titles.push a.text
$('div.score.unvoted').each (div) -> scores.push div.rawtext
@exit 'Title / score mismatch' if scores.length isnt titles.length
for score, i in scores
if score is '•' then continue
@assert(score).isInt()
output.push '[' + score + '] ' + titles[i]
@emit output
@class = Reddit
@job = new Reddit({timeout:10})