JavaScript data formatting/pretty printer

Question

I'm trying to find a way to "pretty print" a JavaScript data structure in a human-readable form for debugging.

I have a rather big and complicated data structure being stored in JS and I need to write some code to manipulate it. In order to work out what I'm doing and where I'm going wrong, what I really need is to be able to see the data structure in its entirety, and update it whenever I make changes through the UI.

All of this stuff I can handle myself, apart from finding a nice way to dump a JavaScript data structure to a human-readable string. JSON would do, but it really needs to be nicely formatted and indented. I'd usually use Firebug's excellent DOM dumping stuff for this, but I really need to be able to see the entire structure at once, which doesn't seem to be possible in Firebug.

Answer 1

Use Crockford's JSON.stringify like this:

var myArray = ['e', {pluribus: 'unum'}];
var text = JSON.stringify(myArray, null, '\t'); //you can specify a number instead of '\t' and that many spaces will be used for indentation...

Variable text would look like this:

[
  "e",
   {
      "pluribus": "unum"
   }
]

---

By the way, this requires nothing more than that JS file - it will work with any library, etc.

Answer 2

I wrote a function to dump a JS object in a readable form, although the output isn't indented, but it shouldn't be too hard to add that: I made this function from one I made for Lua (which is much more complex) which handled this indentation issue.

Here is the "simple" version:

function DumpObject(obj)
{
  var od = new Object;
  var result = "";
  var len = 0;

  for (var property in obj)
  {
    var value = obj[property];
    if (typeof value == 'string')
      value = "'" + value + "'";
    else if (typeof value == 'object')
    {
      if (value instanceof Array)
      {
        value = "[ " + value + " ]";
      }
      else
      {
        var ood = DumpObject(value);
        value = "{ " + ood.dump + " }";
      }
    }
    result += "'" + property + "' : " + value + ", ";
    len++;
  }
  od.dump = result.replace(/, $/, "");
  od.len = len;

  return od;
}

I will look at improving it a bit.
Note 1: To use it, do od = DumpObject(something) and use od.dump. Convoluted because I wanted the len value too (number of items) for another purpose. It is trivial to make the function return only the string.
Note 2: it doesn't handle loops in references.

EDIT

I made the indented version.

function DumpObjectIndented(obj, indent)
{
  var result = "";
  if (indent == null) indent = "";

  for (var property in obj)
  {
    var value = obj[property];
    if (typeof value == 'string')
      value = "'" + value + "'";
    else if (typeof value == 'object')
    {
      if (value instanceof Array)
      {
        // Just let JS convert the Array to a string!
        value = "[ " + value + " ]";
      }
      else
      {
        // Recursive dump
        // (replace "  " by "\t" or something else if you prefer)
        var od = DumpObjectIndented(value, indent + "  ");
        // If you like { on the same line as the key
        //value = "{\n" + od + "\n" + indent + "}";
        // If you prefer { and } to be aligned
        value = "\n" + indent + "{\n" + od + "\n" + indent + "}";
      }
    }
    result += indent + "'" + property + "' : " + value + ",\n";
  }
  return result.replace(/,\n$/, "");
}

Choose your indentation on the line with the recursive call, and you brace style by switching the commented line after this one.

... I see you whipped up your own version, which is good. Visitors will have a choice.