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Lessons JavaScript Error Handling using Try...Catch Bookmark and Share
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Error handling in JavaScript is done through the use of the try...catch statement. The try statement marks a block of statements, expected to generate error(s) and the catch statement provides code handle the error(s).

The type of error that we can handle through the use of try...catch statements, are referred to as Exceptions in JavaScript. When an error of such kind is generated we say that an exception has been thrown. The catch part of the try...catch statement then catches such exception(s).

Besides using the try...catch statement to handle errors we also have the onError event in JavaScript to handle errors. In this lesson we will learn to use the try...catch statement. The onError event will be discussed lated.

More formally the try...catch statement allows us to test a block of code for errors and write code for error handling, if one is found. The syntax of try...catch statement follows:

try
{
//code, expected to generate error, goes here
}
catch(error)
{
//Error handling code goes here
}


The code example below illustrate the usage of try...catch statement:

<html>
<head>
<script type="text/JavaScript">
function printMessage()
{
try
{
aletr("Hello World! "); // alert() function delibrately misspelled
alert("This line is not executed"); // this line of code will not be executed
}
catch(error)
{
alert("There was an error on this page." + error.description);
}
}
</script>
</head>

<body>
<input type="button" value="Greetings" onclick="printMessage()" />
</body>

</html>


The code in the try block above throws an exception, due to the misspelling of the alert(), written as alert(), which is then handled by the catch block. The catch block alert the user about the error. Remember that any code after the error generating line of code in the try block does not execute. The error argument in the parenthesis of the catch clause is a built-in JavaScript object that contains information about the error.


Next >>> Lesson No. 31: JavaScript throw Statement







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