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Is it possible to programatically catch JavaScript SyntaxErrors?

Answer 1

A:

Google has released their Closure toolset which includes a JavaScript compiler and minimizer. I haven't used it personally but have heard a lot of great things. Also, it apparently helps you locate browser compatibility issues.

I don't think it will help you to perform real-time analysis, but still could be a valuable tool.

David Lively 2010-03-26 19:29:23

Answer 2

+1 A:

If you are comfortable with the security exposure, you could call eval() on the code in question to detect syntax errors.

function say(x) { ... emit message in some way.... }

var scriptlets = [
    "foof1 = function(a) {if (a == 7) { return \"A-OK\"; } } ",
    "foof2 = function (a) {if argle bargle seventy 7, then this isn't going to work}"
];

function verifyScriptlet(n) {
    var s = scriptlets[n];
    try {
        var x = eval(s);
        say("verified #"+ n +", result: " + (typeof x));
    }
    catch (exc1)
    {
        say("Exception while verifying #"+ n +": " + exc1.message);
    }
}

verifyScriptlet(0);
verifyScriptlet(1);

Cheeso 2010-03-26 19:39:42

Interesting. Although I'm not particularly comfortable with the security exposure, this is definitely one way to go. Points for that.

Matty 2010-03-26 19:46:06

Answer 3

+1 A:

Generally, a programming language is parsed, and if that succeeds possibly compiled to another form, and if that succeeds then interpreted/executed on hardware or a vm. Just because code passes one phase, doesn't mean it's valid code.

You are asking if code running in the last phase, can be aware of problems encountered in the first part and deal with it.

Some languages offer various hooks into it's own parsing and compiling mechanism. As Cheeso mentioned, eval is Javascript's way of calling into this mechanism.

Rather than wrapping all of your scripts in strings, it might be nicer to leave them in javascript files, and load them into your main program with the following javascript (or similar).

 function load(file){
    var client = new XMLHttpRequest();
    client.open("GET", file, false);
    client.send(null);
    return client.responseText;
  }

  function include(file){
    try {
      eval(load(file));
    } catch (e) {
       alert("problem with file " + file);
    }
  }

z5h 2010-03-26 19:59:23

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Is it possible to programatically catch JavaScript SyntaxErrors?

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