Javascript eval() Exception - line number

Question

In JavaScript I have a var str = ".a long string that contains many lines..." In case of exception that caused by eval(str);

I had like to catch it and print the the line number that caused the exception. (the line internal to str..)

Is it possible?

EDIT As part of the Alligator project (http://github.com/mrohad/Alligator), an application server for JavaScript, I am reading files from the disk and eval() anything that is nested to a scriplet( < ? ? > )

I am running this script outside a browser, using NodeJS (on top of V8).

Not sure this can be done at all without splitting the multi-line command into separate instructions and eval() calls. — Pekka
– Pekka, Commented Aug 15, 2010 at 20:01
It's pretty ugly to use "eval" in the first place. Perhaps you could describe what you're trying to do, and somebody might have a better idea. — Pointy
– Pointy, Commented Aug 15, 2010 at 20:06
The problem with splitting the eval to multi lines is for example when you have if(cond) <- line #1 {some code} <- line #2, line 1 will throw exception since it depends on line #2 — DuduAlul
– DuduAlul, Commented Aug 15, 2010 at 20:12
I assumed that in an age of AJAX someone would want a solution to this. I am having the same problem — puk
– puk, Commented Oct 22, 2011 at 23:30
@MrOhad - checkout this Google V8 issue code.google.com/p/v8/issues/detail?id=1914 — BMiner
– BMiner, Commented May 30, 2012 at 14:11

Steve Brewer · Accepted Answer · 2010-08-15 20:53:04Z

4

Try adding the try/catch to the string instead of around the eval:

var code = 'try{\nvar c = thisFuncIsNotDefined();\n}catch(e){alert(e.lineNumber);}';

answered Aug 15, 2010 at 20:53

Steve Brewer

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4 Comments

DuduAlul Over a year ago

I thought it's even better than my solution, but I have tested it and it doesn't work, same stack as if the try{} catch{} wasn't part of the eval

Michael Over a year ago

combine this with the solution from @AndreyKo and you have a solution that will work in Firefox

Michael Over a year ago

also doesn't work if the string has a syntax error, because the try/catch isn't even able to be constructed properly to catch the error!

Serg Over a year ago

The question was about NodeJS with which this answer doesn't work. e.lineNumber is undefined there.

AndreyKo · Accepted Answer · 2010-08-15 20:30:53Z

3

1) Run:

var javascript_offset;
try {
  undefined_function();
} catch(ex1) {
  javascript_offset = ex1.lineNumber;
}
try {
  YOUR_STRING_WITH_JS
} catch (ex2) {
  var line_that_caused_it = ex2.lineNumber - javascript_offset -2;
  HANDLE_THE_EXCEPTION_HERE
}

edited Aug 15, 2010 at 20:30

answered Aug 15, 2010 at 20:21

AndreyKo

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1 Comment

DuduAlul Over a year ago

I am running this script outside a browser, using NodeJS (on top of V8)

DuduAlul · Accepted Answer · 2010-08-15 21:07:42Z

3

I found a solution which is pretty inefficient, yet I only use it when debug_mode==1 so it's not that bad..

I write the eval_str to a file, I "import that file, and invoke it inside a try{}catch{} and I parse the error line from the stack trace...

In my specific case, this is how the code looks like:

var errFileContent = "exports.run = "+evalStringAsAFunction+";";
fs.writeFile('/home/vadmin/Alligator/lib/debugging.js', errFileContent, function (err) {
    var debug = require('./debugging');
    try{
         debug.run(args...);
    }
    catch(er){
         log.debug(parseg(er));
    }
});

answered Aug 15, 2010 at 21:07

DuduAlul

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1 Comment

BMiner Over a year ago

This is an inefficient hack, but it's definitely a workaround until Google V8 supports this feature. Nice, thx.

杨一涵 · Accepted Answer · 2023-02-23 07:46:18Z

0

replaceErrors(key, value) {
    if (value instanceof Error) {
      var error = {};
      Object.
        getOwnPropertyNames(value).
        forEach(function (key) {
          error[key] = value[key];
        });
      return error;
    }
    return value;
  }
const errorStr = JSON.stringify(error.stack, this.replaceErrors);
const regexp = 'your reg';
          let isHasLineNum = regexp.exec(errorStr);
          let lineNum
          if (isHasLineNum) {
            lineNum = isHasLineNum[0];
          }

answered Feb 23, 2023 at 7:46

杨一涵

11 bronze badge

2 Comments

杨一涵 Over a year ago

harrymoreno.com/2017/02/25/…

Tyler2P Over a year ago

Your answer could be improved by adding more information on what the code does and how it helps the OP.

Topera · Accepted Answer · 2010-08-15 20:19:45Z

-2

This solves your problem?

try {
    eval(str);
} catch (e) {
    console.log(e.lineNumber)
}

answered Aug 15, 2010 at 20:19

Topera

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9 Comments

Christian C. Salvadó Over a year ago

@MrOhad, the lineNumber property on Error objects is non-standard, it will work only on Mozilla implementations, but I'm afraid that it will return you the line number where you invoked eval, not the actual line number inside the evaluated text.

Gert Grenander Over a year ago

Works in Firefox, but not other browsers. In Chrome/Iron, you can get the row number close to the end of e.stack.

DuduAlul Over a year ago

e.stack doesn't return undefined yet it does return the line of the eval and not the line internal to the eval string

AndreyKo Over a year ago

Can you say what does e contain?

BMiner Over a year ago

This answer is incorrect. The question asks if you can get the line number inside the eval'ed text, not the line number where eval() was called.

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