The try statement lets you test a block of code for errors.
The catch statement lets you handle the error.
The throw statement lets you create custom errors.
When the JavaScript engine is executing JavaScript code, different errors can occur:
It can be syntax errors, typically coding errors or typos made by the programmer.
It can be misspelled or missing features in the language (maybe due to browser differences).
It can be errors due to wrong input, from a user, or from an Internet server.
And, of course, it can be many other unforeseeable things.
When an error occurs, when something goes wrong, the JavaScript engine will normally stop, and generate an error message.
The technical term for this is: JavaScript will throw an error.
The try statement allows you to define a block of code to be tested for errors while it is being executed.
The catch statement allows you to define a block of code to be executed, if an error occurs in the try block.
The JavaScript statements try and catch come in pairs.
try
{
//Run some code here
}
catch(err)
{
//Handle errors here
}
In the example below we have deliberately made a typo in the code in the try block.
The catch block catches the error in the try block, and executes code to handle it:
<!DOCTYPE html>
<html>
<head>
<script>
var txt="";
function message()
{
try
{
adddlert("Welcome guest!");
}
catch(err)
{
txt="There was an error on this page.\n\n";
txt+="Error description: " + err.message + "\n\n";
txt+="Click OK to continue.\n\n";
alert(txt);
}
}
</script>
</head>
<body>
<input type="button" value="View message" onclick="message()">
</body>
</html>