246996016-HTML5-Step-by-Step

JavaScript Events and jQuery 297
You’ve now seen how to download jQuery, connect it to your page, and use it to select
elements. And you just looked at a bonus example of a built-in function in jQuery called
.fadeOut(). This leads to a more generalized discussion of functions in jQuery and Java
Script. I promise that we’ll get to the cool stuff soon.
Calling Functions with JavaScript
Functions are groupings of code that perform a task. Here’s a function:
function doSomething() {
alert("Hello World");
}
That’s it, that’s all there is to functions. Well, almost. But there’s no reason to clutter the
discussion of functions when a simple example will suffice. The .fadeOut() example gave
you a glimpse at another important part of a function: a function argument. A function
argument is a value that is passed to the function that determines how or what the function
should do as it carries out its designed task. The .fadeOut() function uses the duration
argument (passed as 5000 in the example at the end of the preceding section) to set
the length of time that the function waits before it fades the element out.
For example, here’s a showAlert() function that accepts a single argument called alertText,
and then shows it in an alert dialog box:
function showAlert(alertText) {
alert(alertText);
}
Calling or invoking the function looks like this:
showAlert("Showing an alert is fun and easy.");
One other important aspect of functions is that they can return a value. Typically, the
return value would be the result of whatever the function accomplishes, although
the return value can be whatever you’d like it to be. For now, you’ll work on a typical
example, where the return value is the logical result of the function. In this next example,
the function adds two numbers and returns the result.
function addTwo(num1, num2) {
var result = num1 + num2;
return result;
}