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<title>Example: Reusing a JSONPRequest Instance to Poll a Remote Server</title>
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<h1>Example: Reusing a JSONPRequest Instance to Poll a Remote Server</h1>
<div class="yui3-g">
<div class="yui3-u-3-4">
<div id="main">
<div class="content"><style scoped>
#out {
margin-top: 2em;
}
#out h4 {
border-right: 100px solid #ccc;
}
</style>
<div class="intro">
<p>
This example shows how to create a reusable JSONPRequest for polling as
well as how to configure success and failure callbacks. See the API
docs and user guide for a full listing of available configurations.
</p>
<p>
For this example, we will use a JSONP service hosted on <a
href="http://yuilibrary.com">YUILibrary</a> to fetch information about
a random Gallery module and render some of the information on the page.
</p>
</div>
<div class="example yui3-skin-sam">
<div id="demo">
<input type="button" id="start" value="Start polling">
<input type="button" id="stop" value="Stop polling">
<div id="out">
</div>
</div>
<script>
YUI().use("jsonp", "transition",function (Y) {
var url = "http://yuilibrary.com/gallery/api/random?callback={callback}",
outputDiv = Y.one("#out"),
gallery;
// Using the configuration object syntax
gallery = new Y.JSONPRequest(url, {
on: {
success: function (response) {
var module = response.modules[0],
author = module.owner;
// Some users don't have a rank
if (!author.rank) {
author.rank = "user";
}
// Format the author info and store as a property of the
// module object for use by Y.Lang.sub
// ('this' refers to the JSONPRequest object by default)
module.authorHTML = Y.Lang.sub(this.authorTemplate, author);
outputDiv.setHTML(Y.Lang.sub(this.moduleTemplate, module));
// Add some flare to the poll interval by showing a "time left"
// indicator via the header's border
Y.one("#out h4")
.setStyle("borderRightWidth", "100px")
.transition({
borderRightWidth: 0,
duration: 7
}, function () {
if (gallery.polling) {
gallery.send();
}
});
},
failure: function () {
gallery.polling = false;
outputDiv.setHTML(this.failureTemplate);
// Wire up the Try again button
outputDiv.one("button").on("click", function () {
gallery.send();
});
}
}
});
gallery.moduleTemplate =
'<h4><a href="{url}">{title}</a></h4>' +
'<p class="author">{authorHTML}</p>' +
'<div>{summary}</div>';
gallery.authorTemplate =
'<img src="{icon}" height="30" width="30">' +
' {fullname} <span class="rank">({rank})</span>';
gallery.failureTemplate =
'<p class="error">Ack, I couldn\'t reach the Gallery web service!</p>' +
'<button>Try again</button>';
gallery.polling = false;
// Click the button to send the JSONP request
Y.one("#start").on("click", function (e) {
if (!gallery.polling) {
gallery.polling = true;
gallery.send();
}
});
Y.one("#stop").on("click", function (e) {
gallery.polling = false;
});
});
</script>
</div>
<h3>The data</h3>
<p>The structure of the JavaScript object returned from YUILibrary's JSONP service will look like this:</p>
<pre class="code prettyprint">{
modules: [
{
url: (the url to the module),
title: (the title of the module),
summary: (short description of the module),
...,
owner: {
icon: (url to the author's thumb image),
fullname: (the author's full name),
rank: (YUI Team member?, Contributor? etc),
...
}
}
],
...
}</pre>
<p>We'll use these objects to populate an HTML template with data <em>{placeholder}</em>s using <code>Y.Lang.sub( template, object )</code>.</p>
<h3>Start simple</h3>
<p>To make a single call to the YUILibrary Gallery API, we can just use</p>
<pre class="code prettyprint">Y.jsonp("http://yuilibrary.com/gallery/api/random?callback={callback}", handleJSONP);</pre>
<p>But since each call to <code>Y.jsonp()</code> creates a new instance of <code>Y.JSONPRequest</code>, we may as well store the instance and reuse it.</p>
<pre class="code prettyprint">var gallery = new Y.JSONPRequest("http://yuilibrary.com/gallery/api/random?callback={callback}", handleJSONP);
gallery.send();</pre>
<h3>Add polling</h3>
<p>JSONPRequest doesn't have any built-in polling mechanism, but <code>Y.later()</code> can handle this for us.</p>
<pre class="code prettyprint">var url = "http://yuilibrary.com/gallery/api/random?callback={callback}";
function handleJSONP(response) {
// populate template from the response object and add to the output div
...
Y.one("#out").setHTML( Y.Lang.sub(template, module) );
// After 7 seconds, call the API for a new module
Y.later(7000, this, this.send);
};
var gallery = new Y.JSONPRequest(url, handleJSONP);
gallery.send();</pre>
<h3>Add failure protection</h3>
<p>In case the Gallery API is busy or some other problem arises, we'll also want to handle this case and display an error. We can do this by passing a configuration object as the second parameter rather than a simple success callback.</p>
<pre class="code prettyprint">var gallery = new Y.JSONPRequest(url, {
on: {
success: function (response) {
// populate output div from the template and response object
...
Y.one("#out").setHTML( Y.Lang.sub(template, module) );
// After 7 seconds, call the API for a new module
Y.later(7000, this, this.send);
},
failure: function () {
Y.one("#out").setHTML( failureTemplate );
}
}
});
gallery.send();</pre>
<h3>Add flare</h3>
<p>Now we'll add a bit of flourish, by adding a visual indicator of how long until the next module is requested. We'll replace the call to <code>Y.later()</code> with a call to <code>node.transition()</code> using a shrinking border to show the remaining time. Then when the transition is complete, we call <code>send()</code> again.
<pre class="code prettyprint">var gallery = new Y.JSONPRequest(url, {
on: {
success: function (response) {
// populate output div from the template and response object
...
Y.one("#out").setHTML( Y.Lang.sub(template, module) );
// Add some flare to the poll interval by showing a "time left"
// indicator via the header's border
Y.one("#out h4")
.setStyle("borderRightWidth", "100px")
.transition({
borderRightWidth: 0,
duration: 7
}, function () {
gallery.send();
});
},
failure: function () {
Y.one("#out").setHTML( failureTemplate );
}
}
});
gallery.send();</pre>
<h3>Stop the poll</h3>
<p>The final step is to add the ability to start and stop the polling. We'll manage this by adding a property to the <code>gallery</code> JSONPRequest instance named <code>gallery.polling</code>. See the full code listing below for the implementation.
<h3 id="fullcode">Full Code Listing</h3>
<h4>HTML</h4>
<pre class="code prettyprint"><div id="demo">
<input type="button" id="start" value="Start polling">
<input type="button" id="stop" value="Stop polling">
<div id="out">
</div>
</div></pre>
<h4>JavaScript</h4>
<pre class="code prettyprint"><script>
YUI().use("jsonp", "transition",function (Y) {
var url = "http://yuilibrary.com/gallery/api/random?callback={callback}",
outputDiv = Y.one("#out"),
gallery;
// Using the configuration object syntax
gallery = new Y.JSONPRequest(url, {
on: {
success: function (response) {
var module = response.modules[0],
author = module.owner;
// Some users don't have a rank
if (!author.rank) {
author.rank = "user";
}
// Format the author info and store as a property of the
// module object for use by Y.Lang.sub
// ('this' refers to the JSONPRequest object by default)
module.authorHTML = Y.Lang.sub(this.authorTemplate, author);
outputDiv.setHTML(Y.Lang.sub(this.moduleTemplate, module));
// Add some flare to the poll interval by showing a "time left"
// indicator via the header's border
Y.one("#out h4")
.setStyle("borderRightWidth", "100px")
.transition({
borderRightWidth: 0,
duration: 7
}, function () {
if (gallery.polling) {
gallery.send();
}
});
},
failure: function () {
gallery.polling = false;
outputDiv.setHTML(this.failureTemplate);
// Wire up the Try again button
outputDiv.one("button").on("click", function () {
gallery.send();
});
}
}
});
gallery.moduleTemplate =
'<h4><a href="{url}">{title}</a></h4>' +
'<p class="author">{authorHTML}</p>' +
'<div>{summary}</div>';
gallery.authorTemplate =
'<img src="{icon}" height="30" width="30">' +
' {fullname} <span class="rank">({rank})</span>';
gallery.failureTemplate =
'<p class="error">Ack, I couldn\'t reach the Gallery web service!</p>' +
'<button>Try again</button>';
gallery.polling = false;
// Click the button to send the JSONP request
Y.one("#start").on("click", function (e) {
if (!gallery.polling) {
gallery.polling = true;
gallery.send();
}
});
Y.one("#stop").on("click", function (e) {
gallery.polling = false;
});
});
</script></pre>
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<div class="hd">
<h2 class="no-toc">Examples</h2>
</div>
<div class="bd">
<ul class="examples">
<li data-description="Get basic GitHub user info using a Y.jsonp(url, callback).">
<a href="jsonp-github.html">Getting Cross Domain JSON Data Using Y.jsonp()</a>
</li>
<li data-description="Create a reusable JSONPRequest object to poll the YUILibrary.com Gallery web service, fetching info on a random Gallery module.">
<a href="jsonp-gallery.html">Reusing a JSONPRequest Instance to Poll a Remote Server</a>
</li>
</ul>
</div>
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<h2 class="no-toc">Examples That Use This Component</h2>
</div>
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<ul class="examples">
<li data-description="Wrapping async transactions with promises">
<a href="../promise/basic-example.html">Wrapping async transactions with promises</a>
</li>
<li data-description="Extend Y.Promise to create classes that encapsulate standard transaction logic in descriptive method names">
<a href="../promise/subclass-example.html">Subclassing Y.Promise</a>
</li>
</ul>
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