(public).sospep.subjects ~ view article ~ 008-callback

<h1 style="text-align: center;">callback - overview</h1>
<h2>[WHAT]</h2>
<ol>
<li>[] a 'callback' refers to a function that we are passing into another function as an arguement.&nbsp;</li>
</ol>
<h2>[WHY]</h2>
<ol>
<li>[] the callback function that we pass into the calling function(aka the callee), will be executed once the callee function has completed execution.&nbsp; <em></em></li>
</ol>
<h2>[WHERE]</h2>
<ol>
<li><strong>[] <a href="/view/article?id=1765" target="_blank">callback</a></strong> - a primer on using callbacks,</li>
</ol>
<h2>[WHEN]</h2>
<ol>
<li>[] to use a callback - when you want to execute another function immediately after the current function has completed its own execution</li>
</ol>
<h2>[EXAMPLE]</h2>
<ol>
<li><strong>first function</strong></li>
</ol>
<div>getDirectionsToLocation(callback){</div>
<div>&nbsp;&nbsp; var directions = "head 4 miles east, turn right at stop sign.Then head 2mile west. location is on left hand side of road"</div>
<div>&nbsp;&nbsp; callback;</div>
<div>}</div>
<div><ol>
<li><strong>second function</strong></li>
</ol></div>
<div>travelToLocation(){</div>
<div>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</div>
<div>}</div>
<div>getDirectionsToLocation(travelToLocation);</div>
<h2>[HOW-TO]</h2>
<ol>
<li><strong>] pass a callback by reference</strong></li>
<ol>
<li>] in the above example we passed the callback arguement(doSomethingMore) by reference,</li>
</ol>
<li><strong>] pass a callback by value</strong></li>
<ol>
<li>] we can also pass callback arguements by value, aka we are passing the function body as the arguement</li>
<li>] doSomething(function(){console.log name;})</li>
</ol></ol>
<h2>[REFERENCE]</h2>
<ol>
<li>]</li>
</ol>
<div>( aka higher order function)</div>
<div><ol>
<li>// PASTE the first function into your javascript console and execute it, nothing will happen</li>
<li>] function doSomething(){</li>
<li>&nbsp;&nbsp;&nbsp; var&nbsp;message = "hello";</li>
<li>}</li>
<li>// PASTE the following function,</li>
<li>] function doSomethingMore(){</li>
<li>&nbsp;&nbsp; console.log name;</li>
<li>// PASTE the following function call into the console window and run it, CONGRATS you just created your first callback</li>
<li>] doSomething(doSomethingMore);</li>
</ol></div>

~ view article ~ Chapter] ch-002-learning-javascript FROM [ Book] language-javascript IN [ libraries] technology-developer-www