Version 14 (modified by cho45, 5 years ago)

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JSDeferred

Simple and clean asynchronous processing.

Sample

http://svn.coderepos.org/share/lang/javascript/jsdeferred/trunk/sample.html

Download

For userscript

Copy and paste following at end of userscript: 

with (D()) {

next(fun...);

// normal xhr
http.get("...").
next(fun...);

// cross site
xhttp.get("...").
next(fun...);

}

// pasted code
function D () {
...JSDeferred...
}

see http://svn.coderepos.org/share/lang/javascript/jsdeferred/trunk/binding/userscript.js to get more information of utility functions (http.get/xhttp.get)

Documentation

See source.

http://svn.coderepos.org/share/lang/javascript/jsdeferred/trunk/doc/index.html

Test

http://svn.coderepos.org/share/lang/javascript/jsdeferred/trunk/test.html

License

MIT. See header of http://svn.coderepos.org/share/lang/javascript/jsdeferred/trunk/jsdeferred.js

Concept

  • Compact
  • Greasemonkey friendly (standalone and compact...)
  • Method chain
  • Short and meaning function name
  • Useful shorthand ways

Internal

This sections use some words as following meanings.

chain
a sequence of processes.
child
the Deferred which returns from a callback.
Deferred#foobar
Deferred.prototype.foobar

Deferred structure and chain structure

A Deferred object has only one callback as its process. Deferred object packages a process (function) as callback and has reference to next Deferred (this is thought like continuation).

Example for understanding Deferred structure. 

var d1 = new Deferred();
d1.callback.ok = function () {
    alert("1");
};

var d2 = new Deferred();
d2.callback.ok = function () {
    alert("2");
};

// Set d2 as continuation of d1.
d1._next = d2;

// Invoke the chain.
d1.call();

And example for usual use. 

next(function () { // this `next` is global function
    alert("1");
}.
next(function () { // this `next` is Deferred#next
    alert("2");
}).
next(function () {
    alert("3");
});

Deferred#next creates new Deferred, sets the passed functions to process of the new Deferred, sets it as continuation of this and returns it.

This structure makes easy to chain child Deferreds. 

next(function () {
    alert("1");
}).
next(function () {
    alert("2");
    // child Deferred
    return next(function () {
        alert("3");
    });
}).
next(function () {
    alert("4");
});

When the callback returns Deferred, the Deferred calling the callback only sets its continuation (_next) to returned Deferred's continuation. 

next(function () {
    alert("1");
}).
next(function () {
    alert("2");
    var d = next(function () {
        alert("3");
    });
    d._next = this._next;
    this.cancel();
}).
next(function () {
    alert("4");
});

After the process, above code is same as following: 

next(function () {
    alert("1");
}).
next(function () {
    alert("2");
    next(function () {
        alert("3");
    }).
    next(function () {
        alert("4");
    });
});

http://f.hatena.ne.jp/images/fotolife/c/cho45/20071207/20071207014817.png

Error processing and recovering

A Deferred has also error-back for error processing. Let's just see a example (from test): 

next(function () {
    throw "Error";
}).
error(function (e) {
	expect("Errorback called", "Error", e);
	return e; // recovering error
}).
next(function (e) {
	expect("Callback called", "Error", e);
	throw "Error2";
}).
next(function (e) {
	// This process is not called because
	// the error is not recovered.
	ng("Must not be called!!");
}).
error(function (e) {
	expect("Errorback called", "Error2", e);
});

The error thrown in callback is propagated by error-back chain. If the error-back returns normal value, the error is considered as recovery, and the callback chain continues.

Deference between MochiKit? and JSDeferred

  • MochiKit? Deferred has chain by Array. JSDeferred has chain by chain of Deferred.
  • MochiKit? Deferred separates parent chain and child chain, JSDeferred not.