Got your callback

Developer
Nick Williams
Size
2,451 Kb
Views
30,360
  1. Got your callback Previews
  2. Got your callback HTML Codes
  3. Got your callback JS Codes

How do I make an got your callback?

What is a got your callback? How do you make a got your callback? This script and codes were developed by Nick Williams on 27 August 2022, Saturday.

Got your callback Previews
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Got your callback - Script Codes HTML Codes

<!DOCTYPE html>
<html >
<head> <meta charset="UTF-8"> <title>got your callback</title>
</head>
<body> <script src="js/index.js"></script>
</body>
</html>

Got your callback - Script Codes JS Codes

var someArray = [5,6,7,8,9];
// first let's write a really naive function
// that loops through the above array and
// prints them numbers out
function each(collection) { var item; for(item in collection) { if(collection.hasOwnProperty(item)) { // assuming callback was a function, // call it and pass in the item console.log(collection[item]); } }
}
each();
// this does the job, but it's a bit crap. It's
// really inflexible, because it can only log
// to console, what if we wanted to do other things?
// We want to be able to modify functionality without
// changing the core code itself.
// Enter callbacks!
// Modern JS engines have a forEach method on
// the array prototype, so you can do stuff like
// [1,2,3,4,5].forEach(callback)
// Let's use it and pass in a callback to
// log the numbers to the console, replicating the
// functionality above.
someArray.forEach(function(item) { console.log(item);
});
// This of course has accepted a callback.
// So mimicing this functionality is a good
// lesson in writing code that has callbacks.
// Let's do that now...
function each(collection, callback) { var item; for(item in collection) { if(collection.hasOwnProperty(item)) { // now instead of calling console.log, // we call the callback function instead! // we can have the same behaviour as before, // but now it's infinitely more flexible callback(collection[item]); } }
}
// Let's put our function to use, supplying a callback.
// This will give us the same results as we've seen
// before.
each(someArray, function(item) { console.log(item);
});
// The benefit of callbacks is that they give
// a neat extensibility point, where a consumer
// of your API can modify functionality.
// So let's use our callback function to do exactly that
// instead of console.log()
// Remember that all we're doing with callbacks
// is passing a *reference* to a function to another
// function, as an argument. This means that we can
// pass references with anonymous functions
// (as above), variables, or named functions
// using a function reference stored in a variable
var functionReference = function(item) { console.warn(item);
};
each(someArray, functionReference);
// using a named function
function namedFunction(item) { console.error(item);
}
each(someArray, namedFunction);
// the same principle applies when the code is
// asynchronous too. It just means the callback
// happens at a later time (in fact, JS necessitates the
// use of callbacks for asynchronous code.
// Think about event handlers, setTimeout etc.
// they're basically all given callbacks, which get
// invoked in response to some event (click, timer etc)
Got your callback - Script Codes
Got your callback - Script Codes
Home Page Home
Developer Nick Williams
Username WickyNilliams
Uploaded August 27, 2022
Rating 3
Size 2,451 Kb
Views 30,360
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