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Handling Errors

It is possible to have the JavaScript console come up whenever there is an error by going into Tools

Preferences, and then clicking on Multimedia. You’ll see a check box titled Enabled JavaScript, along with

a button labeled JavaScript Options..... If you click the button, a new dialog pops up (see Figure 14-9), one

of the options is Open JavaScript Console on Error. When this check box is checked (it is unchecked by

default), the JavaScript console pops up whenever there is an error.

Figure 14-9

Handling Errors

Understanding errors is just part of the solution; understanding how to handle those errors is the other

part. Instead of using multiple

if..else

statements, JavaScript offers two specific ways to handle

errors. The Browser Object Model includes the

onerror

event handler on both the window object and

on images, whereas ECMAScript defines the

try...catch

construct, another statement borrowed from

Java, to deal with exceptions. This section outlines the advantages and disadvantages of each approach.

The onerror event handler

The

onerror

event handler was the first feature to facilitate error handling for JavaScript. The

error

event is fired on the

window

object whenever an exception occurs on the page. Example:

<html>

<head>

<title>OnError Example</title>

window.onerror = function () {

alert(“An error occurred. “);

}

</script>

</head>

</body>

</html>

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Error Handling

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