How to detect console error in Javascript (due to syntax error)

Question

I'm trying to detect when a console error occurs. I've looked here and have seen 2 suggestions

window.onerror and try catch

The following demonstrates an issue where this is not "caught" (by caught, as per the code below, I'd expect to see an alert and I do not).

window.onerror = function(error) {
    alert("window error..." + error );
}

    const arr = [];

try{
    arr.push({
        'firstValue':'Me 'And' You',
        'otherValue':5
    });
}catch(err){
    alert("Error..." + err);
}

The part causing the issue is

'firstValue':'Me 'And' You',

The reason for this is how this line of code is generated and I suspect the real fix is to correct this (using MVC.NET Razor)

'firstValue': '@Model.MyStringWithNoFormattingOrChecking'

Where the value of MyStringWithNoFormattingOrChecking is Me 'And' You

However, my question is about why the onerror or try catch didn't work. Or what I could have done to have caught this using javascript (I don't actually show an alert, I log via Ajax)

Syntax errors are not catched at runtime, since a code having a syntax error is never executed. — Teemu
– Teemu, Commented Jan 23, 2018 at 11:50
I don't think you can catch plain syntax errors like that with javascript. The parser will stop after the 'Me ' — baao
– baao, Commented Jan 23, 2018 at 11:50
@baao, if I'm using the wrong tool/tech, then that is fine. What could I use instead of JavaScript then? — MyDaftQuestions
– MyDaftQuestions, Commented Jan 23, 2018 at 11:51
You need to properly escape the ' within the string. I've never used MVC.NET, so I can't say how to fix the creation of the string - but I'd look there first instead of on the js part — baao
– baao, Commented Jan 23, 2018 at 11:52
This is indeed an escaping issue within .NET rather than a JavaScript error handling issue. This article is an excellent summary of the issue at hand. — James Thorpe
– James Thorpe, Commented Jan 23, 2018 at 11:54

Chris Lear · Accepted Answer · 2018-01-23 12:09:36Z

2

Try putting the onerror code in its own script tag, which runs earlier than this syntax error.

This code does what you want

<head>
    <script type="text/javascript">

window.onerror = function(error) {
    alert("window error..." + error );
}
    </script>


    <script type="text/javascript">
const arr = [];

try{
    arr.push({
        'firstValue':'Me 'And' You',
        'otherValue':5
    });
}catch(err){
    alert("Error..." + err);
}
    </script>

</head>

[tested in Firefox, Chome and Edge]

edited Jan 23, 2018 at 12:09

answered Jan 23, 2018 at 12:04

Chris Lear

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