JavaScript Try…Catch Statement

JavaScript¬†Try…Catch¬†Statement

The try…catch statement allows you to test a block of code for errors.


JavaScript – Catching Errors

When browsing Web pages on the internet, we all have seen a JavaScript alert box telling us there is a runtime error and asking “Do you wish to debug?”. Error message like this may be useful for developers but not for users. When users see errors, they often leave the Web page.

This chapter will teach you how to catch and handle JavaScript error messages, so you don’t lose your audience.


The try…catch Statement

The try…catch statement allows you to test a block of code for errors. The try block contains the code to be run, and the catch block contains the code to be executed if an error occurs.

Syntax

try
{
//Run some code here
}
catch(err)
{
//Handle errors here
}

Example 1

The example below is supposed to alert “Welcome guest!” when the button is clicked. However, there’s a typo in the message() function. alert() is misspelled as adddlert(). A JavaScript error occurs. The catch block catches the error and executes a custom code to handle it. The code displays a custom error message informing the user what happened:

<html>
<head>
<script type=”text/javascript”>
var txt=””;
function message()
{
try
{
adddlert(“Welcome guest!”);
}
catch(err)
{
txt=”There was an error on this page.\n\n”;
txt+=”Error description: ” + err.description + “\n\n”;
txt+=”Click OK to continue.\n\n”;
alert(txt);
}
}
</script>
</head>

<body>
<input type=”button” value=”View message” onclick=”message()” />
</body>

</html>

Example 2

<html>
<head>
<script type=”text/javascript”>
var txt=””;
function message()
{
try
{
adddlert(“Welcome guest!”);
}
catch(err)
{
txt=”There was an error on this page.\n\n”;
txt+=”Click OK to continue viewing this page,\n”;
txt+=”or Cancel to return to the home page.\n\n”;
if(!confirm(txt))
{
document.location.href=”http://www.paktutorial.com/”;
}
}
}
</script>
</head>

<body>
<input type=”button” value=”View message” onclick=”message()” />
</body>

</html>

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