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 () {
console.log("Deferred resolved!");
} ).fail( function () {
console.log("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.