can you enumerate local variables?

david_kw · 02-03-2007, 09:28 PM

I was wondering if it is possible to find the names of all the local variables.

Like

Code:

function func() {
  var x = 5;
  var y = 8;

  // some code

  for (key in func.local) {
    alert(key + "=" + func.local['key']);
  }
}

and you'd get two alerts
x=5 and y=8

Is anything like that or similar possible? I know you can get the arguments with the argument[] object.

Thanks,
david_kw

liorean · 02-03-2007, 10:16 PM

Nope. The variable object is not available from script in any way, except for the global object or objects used in with statements.

There have been some JavaScript engines that exposed all locals as named properties of the function object (only while the function was running however), but nothing you can rely on.

chump2877 · 02-03-2007, 10:33 PM

The closest I can think of to acheive something like that is this:

Code:

<script type="text/javascript">

function whatever()
{
  var obj = new Object;

  obj.x = 5;
  obj.y = 8;

  for (var prop in obj)
  {
    alert(prop + "=" + obj[prop]);
  }
}

</script>

<input type="button" value="click me" onclick="whatever();" />

...make the object a local "variable" and iterate through the property/value pairs in the object...

david_kw · 02-03-2007, 11:01 PM

Hmm, bummer. Ok thanks a lot. Saves me a lot of time searching even more for something that doesn't exist.

david_kw

david_kw · 02-04-2007, 06:58 AM

Well I came up with a hack sort of way to do it. In case you are wondering why I wanted this functionality, I am trying to put together a better closure breakpoint (I hate the IE debugger, thank god for FireBug) like

http://trimpath.com/project/wiki/TrimBreakpoint

Basically, I found that arguments.callee is the function, so I do a toString() on it then parse it for variable names. I have no doubt some might slip by my parsing depending on how it is declared, but it seems to get most of them (at least the way I declare them).

Here's the code to parse the function in case you are interested

Code:

function getLocals(args) {
  var ret = [];
  var reArg = /\(?\s*(\w+)\s*(,|\))/g;
  var reHasVar = /\Wvar\W/;
  var reGetVar = /(var|,)\s*(\w+)/g;
  var a = args.callee.toString().split("\n");
  var lookForArgs = true;
  var reResult;

  ret.push(a[0]); // save the function name for later use
  
  for (var i = 0; i < a.length; i++) {
    if (lookForArgs) {
      while ((reResult = reArg.exec(a[i])) != null) {
        ret.push(reResult[1]);
      }
      if (/\{/.test(a[i])) {
        lookForArgs = false;
      }
    }
    if (!lookForArgs) {
      if (reHasVar.test(a[i])) {
        while ((reResult = reGetVar.exec(a[i])) != null) {
          ret.push(reResult[2]);
        }
      }
    }
  }

  return(ret);
}

It's called like
getLocals(arguments);
and returns an array of arguments and local variable names which I can iterate through using eval to get the values.

Thanks again. I imagine without your help I'd still be searching the web for some way it is exposed by the browser.

david_kw

david_kw · 03-14-2007, 08:02 PM

For anyone interested. I fixed a few bugs in my getLocals function and made it more flexible when searching for variables. Here is the code plus a working example.

Code:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html>
  <head>
    <title>Enumerate Local Variables</title>
    <script type="text/javascript">
    /* <![CDATA[ */
      function indexInLiteral(str, index) {
        var inStrLiteral = 0;
        var inObjLiteral = 0;
        var inArrayLiteral = 0;

        for (var i = 0; i < str.length; i++) {
          if (inStrLiteral) {
            if (str.charAt(i) == "'" || str.charAt(i) == '"') {
              inObjLiteral--;
            }
          } else {
            if (str.charAt(i) == "'" || str.charAt(i) == '"') {
              inObjLiteral++;
            }
          }
          if (!inStrLiteral) {
            if (inObjLiteral) {
              if (i == index) {
                return (true);
              }
              if (str.charAt(i) == "}") {
                inObjLiteral--;
              }
            } else {
              if (str.charAt(i) == "{") {
                inObjLiteral++;
              }
            }
            if (inArrayLiteral) {
              if (i == index) {
                return (true);
              }
              if (str.charAt(i) == "]") {
                inArrayLiteral--;
              }
            } else {
              if (str.charAt(i) == "[") {
                inArrayLiteral++;
              }
            }
          }
        }

        return (false);
      }

      function getLocals(args) {
        var ret = [];
        var reArg = /\(?\s*(\w+)\s*(,|\))/g;
        var reEndArg = /\{/;
        var reHasVar = /(\W|^)var\W/;
        var reGetVar = /(var|,)\s*(\w+)/g;
        var a = args.callee.toString().split("\n");
        var lookForArgs = true;
        var reResult;

        ret.push(a[0]); // save the function name for later use
        
        for (var i = 0; i < a.length; i++) {
          if (lookForArgs) {
            reArg.lastIndex = 0;
            while ((reResult = reArg.exec(a[i])) != null) {
              ret.push(reResult[1]);
            }
            reEndArg.lastIndex = 0;
            if (reEndArg.test(a[i])) {
              lookForArgs = false;
            }
          }
          if (!lookForArgs) {
            reHasVar.lastIndex = 0;
            if (reHasVar.test(a[i])) {
              reGetVar.lastIndex = 0;
              while ((reResult = reGetVar.exec(a[i])) != null) {
                if (!indexInLiteral(a[i], reResult.index)) { 
                  ret.push(reResult[2]);
                }
              }
            }
          }
        }

        return (ret);
      }

      var array_of_locals;
      var str, e;
      function doIt(s) { 
        var adiv = document.getElementById("adiv");
        var x = 5, y = 9;
        var re = /^test$/;

        array_of_locals = getLocals(arguments);

        str = "Variables for ";
        for (var i = 0; i < array_of_locals.length; i++) {
          if (i == 0) {
            str += array_of_locals[i] + "<br/>";
          } else {
            str += "&nbsp;&nbsp;" + array_of_locals[i] + " = " + eval(array_of_locals[i]) + "<br/>";
          }
        }

        adiv.innerHTML = str;
      }
    /* ]]> */
    </script>
  </head>
  <body>
    <div>
      <button onclick="doIt('This is junque...');">Do it</button>
      <br />
      <div id="adiv"> </div>
    </div>
  </body>
</html>

david_kw