HTML and CSS Reference
In-Depth Information
The Hands-On Practice 14.6 pops up the prompt box as soon as the page loads. What
if we prefer to allow the user to decide when a particular script should be interpreted or
run by the browser? Perhaps we could use an onmouseover event handler and run the
script when the user moves the mouse pointer over a link or image. Another method,
perhaps more intuitive for the user, is to make use of a button and direct the user to
click the button to run the script. The Web page visitor doesn't need to be aware that a
script will run, but can click a button to initiate some sort of functionality.
Three types of buttons were introduced in Chapter 9:
A submit button <input type="submit" /> is used to submit a form.
A reset button <input type="reset" /> is used to clear values entered on a
The third type of button <input type="button" /> does not have any default
action related to forms.
In this section we will make use of the button <input type="button" /> and the
onclick event handler to run a script. The onclick event handler can run a single
command or multiple commands. A sample follows:
<input type="button" value="Click to see a message"
onclick="alert('Welcome!');" />
In this sample, the button will display the text “Click to see a message.” When the user
clicks the button, the click event occurs and the onclick event handler executes the
alert('Welcome!'); command. The message box appears. This method is very effec-
tive when there is only one JavaScript statement to execute. It quickly becomes unman-
ageable when there are more statements to execute. When that happens, it makes sense
to place all JavaScript statements in a block and somehow point to the block to exe-
cute. If the statement block has a name, we can execute the block by pointing to the
name. In addition to providing a shortcut name, this code is also easily reused. We can
provide a name for a statement block by creating a function.
A function is a block of JavaScript statements with a specific purpose, which can be run
when needed. A function can contain a single statement or a group of statements, and is
defined as follows:
function function_name()
... JavaScript statements
The function definition starts with the keyword function followed by the name of the
function. The parentheses are required, and more advanced functions make use of them.
You can choose a name for the function, just like you choose a name for a variable. The
function name should indicate the purpose of the function somehow. The statements are
contained within the brackets. The block of statements will execute when the function
is called.
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