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Deferred

A port of the jQuery Deferred library to node js.

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