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To hide or not to hide

</body>

</html>

Here, the

tag is used to create a button that calls

sayHi()

when clicked. The

onclick

attribute specifies an

event handler

, which is the code that responds to a given event. Events and event

handlers are discussed further in Chapter 9, “All about Events.”

Note that JavaScript begins running as soon as the page begins loading, so it is possible to call function

that doesn’t exist yet. In the previous example, you can cause an error by placing the original

tag after the function call:

<html>

<head>

<title>Title of Page</title>

</head>

<body>

sayHi();

</script>

<p>This is the first text the user will see.</p>

function sayHi() {

alert(“Hi”);

}

</script>

</body>

</html>

This example causes an error because

sayHi()

is called before it is defined. Because JavaScript is load-

ing top-down, the function

sayHi()

does not exist until the second

tag is encountered.

Be aware of this problem and, as mentioned previously, use events and event handlers to call your

JavaScript functions.

To hide or not to hide

When JavaScript was first introduced, only one browser supported it, so concern arose over how the

nonsupporting browsers would deal with the

tag and the code contained within. To that

end, a format was devised to hide code from older browsers (which is a phrase that can still be found in

the source code of a great many Web sites on the Internet today). The following method uses HTML

comments around inline code so that other browsers won’t render the code to the screen:

function sayHi() {

alert(“Hi”);

}

//-->

</script>

The first line begins an HTML comment immediately after the opening

tag. This works

because the browser still considers the rest of that line as part of HTML, with JavaScript code beginning

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JavaScript in the Browser

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