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Blogged date : 2008 Apr 15
Neil Roberts goes into the XHR Plugins that Dojo uses and how you can extend the system to have your own.
If you look at dojo.xhrGet you will see "Acceptable values are: text (default), json, json-comment-optional, json-comment-filtered, javascript, xml", but:
What you may not know is that the handleAs parameter is merely a way of specifying what plugin to use. Knowing where these plugins are, how they work, and how they can be adapted to suit your project will allow you to make repetitive tasks easy and less error-prone.
He starts by piggybacking on the json style callback, and adds a hook so when you do a query, if there are updated objects out there, they come back in the JSON so you can deal with them without having an extra remote call:
JAVASCRIPT:
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dojo._contentHandlers.json = (function(old){
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return function(xhr){
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var json = old(xhr);
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if(json.updated){
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processUpdatedObjects(json.updated);
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delete json.updated;
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}
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return json;
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}
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})(dojo._contentHandlers.json);
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Next, Neil goes on to write a system that auto updates nodes:
JAVASCRIPT:
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dojo.xhrGet({
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url: "node-updates.php",
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handleAs: "node-update-server"
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});
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dojo.xhrGet({
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url: "node-content.php?node=sidebar",
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node: "sidebar",
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handleAs: "node-update"
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});
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which is as easy as:
JAVASCRIPT:
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dojo.mixin(dojo._contentHandlers, {
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"node-update-server": function(xhr){
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var json = dojo._contentHandlers.json(xhr);
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dojo.forEach(json.updates, function(update){
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var node = dojo.byId(update.id);
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if(node){
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node.innerHTML = update.html;
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}
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});
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},
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"node-update": function(xhr){
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var node = dojo.byId(xhr.args.node);
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if(node){
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node.innerHTML = dojo._contentHandlers.text(xhr);
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}
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}
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});
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In conclusion:
Dojo makes it incredibly easy to change the way that your Ajax calls work. You can change the format of JSON your server returns without having to change any of your callbacks, you can change the handleAs type for a single function to change the data given to your callback, you can get rid of callbacks altogether and use the arguments to your xhr call determine what should be done with your results.
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