Javascript Try/Catch
-
02-07-2019 - |
Question
I've got a function that runs a user generated Regex. However, if the user enters a regex that won't run then it stops and falls over. I've tried wrapping the line in a Try/Catch block but alas nothing happens.
If it helps, I'm running jQuery but the code below does not have it as I'm guessing that it's a little more fundamental than that.
Edit: Yes, I know that I am not escaping the "[", that's intentional and the point of the question. I'm accepting user input and I want to find a way to catch this sort of problem without the application falling flat on it's face.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html>
<head>
<title>Regex</title>
<script type="text/javascript" charset="utf-8">
var grep = new RegExp('gr[');
try
{
var results = grep.exec('bob went to town');
}
catch (e)
{
//Do nothing?
}
alert('If you can see this then the script kept going');
</script>
</head>
<body>
</body>
</html>
Solution
Try this the new RegExp is throwing the exception
Regex
<script type="text/javascript" charset="utf-8">
var grep;
try {
grep = new RegExp("gr[");
}
catch(e) {
alert(e);
}
try
{
var results = grep.exec('bob went to town');
}
catch (e)
{
//Do nothing?
}
alert('If you can see this then the script kept going');
</script>
OTHER TIPS
The problem is with this line:
var grep = new RegExp('gr[');
'[' is a special character so it needs to be escaped. Also this line is not wrapped in try...catch, so you still get the error.
Edit: You could also add an
alert(e.message);
in the catch clause to see the error message. It's useful for all kind of errors in javascript.
Edit 2: OK, I needed to read more carefully the question, but the answer is still there. In the example code the offending line is not wrapped in the try...catch block. I put it there and didn't get errors in Opera 9.5, FF3 and IE7.
var grep, results;
try {
grep = new RegExp("gr[");
results = grep.exec('bob went to town');
}
catch(e) {
alert(e);
}
alert('If you can see this then the script kept going');
putting the RegExp initialization inside the try/catch will work (just tested in FireFox)
var grep, results;
try
{
grep = new RegExp("gr["); // your user input here
}
catch(e)
{
alert("The RegExpr is invalid");
}
// do your stuff with grep and results
Escaping here is not the solution. Since the purpose of this snippet is to actually test a user-generated RegExpr, you will want to catch [ as an unclosed RegExpr container.
your RegExp doesn't close the [
In my FireFox, it never returns from the constructor -- looks like a bug in the implementation of RegExp, but if you provide a valid expression, it works
One option is to validate the user-generated expressions. That is; escape characters that you know will stall your script.