Deferred

jQuery Deferred Library for Node js.

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jQuery Deferred solves the following problems:

• support common deferred interface in node
• give some access to the deferred library underpinning in the browser

Usage :

var Deferred = require('Deferred');
var when = Deferred.when;

var dfd = new Deferred() // || Deferred()
dfd.done( function () {
	alert("Deferred resolved!");
} ).fail( function () {
	alert("Deferred rejected!");
} );

setTimeout( function(){
	dfd.resolve();
}, 1500 );

Slightly more meaningful Usage Case :

var fs = require('fs');

function readFile(fileName){
	var hasReadFile = new Deferred();
	fs.readFile(fileName, 'utf8',function(err, contents){
		if ( err !== null ) {
			return hasReadFile.reject(err);
		}
		return hasReadFile.resolve(contents);
	});
	return hasReadFile.promise();
}

function parseFile(fileName, parser){
	// parser implemented elsewhere
	readFile(fileName)
		.done(parser.parse)
		.fail(function(err){
			console.error('readFile :: ', err);
		});
}

What are Deferreds?

I am putting together a small list of articles worth reading about the concept of deferreds, futures and promises. In it's simplest form a deferred object is a way to introduce a callback stack to a function.

ColonelPanic