In: Root » » AJAX » Implementing the Synchronous Class in Ajax
Another potential solution is to use the synchronous version of XMLHttpRequest. For the most part, I use asynchronous mode, but there are times when synchronous mode is more appropriate. article 1-3 presents an example in which the test cannot continue until the Ajax page has finished loading its content. To implement a Synchronous version of Asynchronous, only the call method needs to be adapted everything else can remain as is. For example, to convert the initial client code to use synchronous mode, you could use the following code:
function LoadAtomFeed() {
var synchronous = new Synchronous();
synchronous.settings = {
onComplete : function(xmlhttp) {
parseAtom( xmlhttp.responseXML);
flexbox.update();
}
}
synchronous.get("/services/blog/entries/current");
}
The bold code shows the only major change: instead of instantiating Asynchronous, it instantiates Synchronous. You still provide a settings code block, and you still call the get function. The reason this approach works is due to the way that Asynchronous and Synchronous are wired together, as illustrated by the following code:
function Asynchronous(userSettings) {
this.xmlhttp = new FactoryXMLHttpRequest();
this.isBusy = false;
this.userSettings = userSettings;
}
Asynchronous.prototype.get = HttpRequest_get;
Asynchronous.prototype.put = HttpRequest_put;
Asynchronous.prototype.del = HttpRequest_delete;
Asynchronous.prototype.post = HttpRequest_post;
Asynchronous.prototype.call = Asynchronous_call;
function Synchronous(userSettings) {
this.xmlhttp = new FactoryXMLHttpRequest();
this.isBusy = false;
this.userSettings = userSettings;
}
Synchronous.prototype.get = HttpRequest_get;
Synchronous.prototype.put = HttpRequest_put;
Synchronous.prototype.del = HttpRequest_delete;
Synchronous.prototype.post = HttpRequest_post;
Synchronous.prototype.call = Synchronous call;
The bold code shows the single change in each class. Notice that this way of defining a class uses a contract. Each type has five functions: get, put, del, post, and call. The four functions get, put, del, and post could be considered a module and thought of as a mixin. Each of the four functions adds value in some way, but relies on a contract where the type contains a call method. The call method is what varies on the Asynchronous and Synchronous types, as each has a unique implementation. The synchronous call implementation is as follows.
Source: /client/scripts/jaxson/communications.js
function Synchronous_call(request) {
var instance = this;
this.xmlhttp.open(request.action, request.url, false,
this.settings.username, this.settings.password);
if (request.headers) {
for( defHeader in request.headers) {
this.xmlhttp.setRequestHeader(defHeader, request.headers[defHeader]);
}
}
if (this.settings.headers) {
for( defHeader in this.settings.headers) {
this.xmlhttp.setRequestHeader(defHeader,
this.settings.headers[defHeader]);
}
}
try {
this.xmlhttp.send(request.data);
if (instance.settings.onComplete) {
instance.settings.onComplete(instance.xmlhttp);
}
}
catch( e) {
globals.errorHandler(e);
}
}
Without going into too much detail, you can see that the implementations are very similar. The only real difference is that calling onComplete after calling the send method mimics the asynchronous calling of the onComplete code block. In synchronous mode, after the send method returns, the state of XMLHttpRequest is valid and calling onComplete is correct. |
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