Page 170 - JavaScript

foo(array, function (x) {
console.log(x);
});

Examples with Asynchronous Functions

In jQuery, the $.getJSON() method to fetch JSON data is asynchronous. Therefore, passing code in
a callback makes sure that the code is called after the JSON is fetched.

$.getJSON() syntax:

$.getJSON( url, dataObject, successCallback );

Example of $.getJSON() code:

$.getJSON("foo.json", {}, function(data) {
// data handling code
});

The following would not work, because the data-handling code would likely be called before the
data is actually received, because the $.getJSON function takes an unspecified length of time and
does not hold up the call stack as it waits for the JSON.

$.getJSON("foo.json", {});
// data handling code

Another example of an asynchronous function is jQuery's animate() function. Because it takes a
specified time to run the animation, sometimes it is desirable to run some code directly following
the animation.

.animate() syntax:

jQueryElement.animate( properties, duration, callback );

For example, to create a fading-out animation after which the element completely disappears, the
following code can be run. Note the use of the callback.

elem.animate( { opacity: 0 }, 5000, function() {
elem.hide();
} );

This allows the element to be hidden right after the function has finished execution. This differs
from:

elem.animate( { opacity: 0 }, 5000 );
elem.hide();

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