How in JavaScript fetch line from which the function was called?

Question

The code below shows my almost complete page source (without doctype) and line number from where test() was called. Because code does not contain doctype then I when I do alert(code[line]) I don't get the right line.

<script>
function test(what)
{
    var err = new Error;
    var line = err.stack.split("\n")[1].split(':')[2];
    var code = document.documentElement.outerHTML.split("\n");
    console.log(code);
    alert(line);
}

test('hello there');
<script>

How do I get 'test('hello there');' from my test function as a string?

The problem is with line numbering. My line returns the correct line number as in the source file, but my code returns page source with different numbering (it misses DOCTYPE and have different line breaks). So the question is: how to get the "real" page source?

use firebug for dubbuging. it will give you all detail by putting break points in your js — Nirav Prajapati
– Nirav Prajapati, Commented Jul 18, 2014 at 12:48
@NiravPrajapati I do use Firebug but I need my function test() to self debug itself (some sort of automatic tests). — Tom
– Tom, Commented Jul 18, 2014 at 12:50
@Tom :: rename your function and try , becuse may be test() is built in function in javascript — Nirav Prajapati
– Nirav Prajapati, Commented Jul 18, 2014 at 12:52

Denys Séguret · Accepted Answer · 2014-07-18 12:59:41Z

A solution is to look not in the whole HTML document but in the right script element. It works but you'd need some care before to use it :

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>JS Bin</title>
</head>
<body>
<script>
  function test(what) {
    var err = new Error;
    console.log(err.stack.split("\n"))
    var line = err.stack.split("\n")[2].split(':')[1];
    var script = document.scripts[0];
    var code = (script.innerText||script.textContent).split(/<br>|\n/);
    console.log(line);
    console.log(code, code.length);
    console.log(code[+line]); // this logs "test('hello there');"
}

test('hello there');
</script>
</body>
</html>

The first thing to do would probably be to give an id to your script element instead of relying on the number.

And I really wouldn't use such a thing apart for some short tests.

Demonstration (click "Run with JS")

Thanks, works fine in Chrome. Trying to fix it for Firefox but seems promising :)

Tom · Accepted Answer · 2014-07-18 13:08:08Z

Here's a working, but ugly solution. Ugly because:
1. Loads the same page again
2. Uses async ajax

<script>
function getSource()
{
    var request = new XMLHttpRequest();

    request.open('GET', location.href, false);
    request.send(null);

    if (request.status === 200) 
    {
        return request.responseText;
    }
    return '';
}
function test(what)
{
    var err = new Error;
    var line = err.stack.split("\n")[1].split(':')[2];
    var code = getSource().split("\n");
    alert(code[line-1]);
}

test('hello there');
</script>

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