JSON.parse(jsonString) is a pure JavaScript approach so long as you can guarantee a reasonably modern browser.

1. Launch Firefox/Chrome/Safari
2. Open Firebug/developer tools
3. Copy/paste your code into the console.

4. Then type console.log(JSON.stringify(object)) and voila!

   {"item1":"value1","item2":1000,"item3":["a","b","c"],
    "item4":[1,2,3],"item5":{"foo":"bar"}}
   

5. Copy/paste back into your text editor.

For more control over the formatting, I have a free online webpage:

http://phrogz.net/JS/NeatJSON

that lets you paste JSON or JS values in one box and see JSON at the bottom, with lots of knobs and sliders to adjust how it looks. For example, the JS value ["foo","bar",{dogs:42,piggies:0,cats:7},{jimmy:[1,2,3,4,5],jammy:3.14159265358979,hot:"pajammy"}] can be formatted like any of the following (and more):

[
    "foo",                            <- adjustable indentation
    "bar",
    {"dogs":42,"piggies":0,"cats":7}, <- small objects on one line!
    {
        "jimmy":[1,2,3,4,5],          <- small arrays on one line!
        "jammy":3.142,                <- decimal precision!
        "hot":"pajammy"
    }
]

[
  "foo",
  "bar",
  { "cats":7, "dogs":42, "piggies":0 }, <- spaces inside braces!
  {
    "hot":"pajammy",                    <- sort object keys!
    "jammy":3.14159265358979,
    "jimmy":[ 1, 2, 3, 4, 5 ]           <- spaces after commas!
  }
]

[ "foo",                           <- 'short' format puts first value
  "bar",                           <- on same line as opening bracket...
  { "dogs"    : 42,
    "piggies" : 0,                 
    "cats"    : 7 },               <- ...and close bracket with last value!
  { "jimmy" : [ 1, 2, 3, 4, 5 ],
    "jammy" : 3.14159265358979,    <- spaces around colons!
    "hot"   : "pajammy" } ]        <- align object values!

All current browsers have native JSON support built in. So as long as you're not dealing with prehistoric browsers like IE6/7 you can do it just as easily as that:

var j = {
  "name": "binchen"
};
console.log(JSON.stringify(j));