recursive JSON.stringify implementation

Question

I am trying to learn recursion in Javascript, so I figured I\'d rewrite the native JSON.stringify function using recursion as a challenge to myself. I almost got my

Answer 1

I disagree with @Bergi's assertion that regular old recursion isn't a good fit for this. Like I said in my comment you can avoid the use of a for loop by passing the index as an argument to the function. This is a very common technique and prevents you from needing to copy or modify the data structure.

Here's my stab at such an implementation. As you can see it's really straightforward (and to my own surprise, it works!):

function jsonify(obj, idx) {
  var json, objStr = toString.call(obj);

  // Handle strings
  if(objStr == '[object String]') { return '"' + obj + '"' }

  idx = idx || 0

  // Handle arrays
  if(objStr == '[object Array]') {
    if(idx >= obj.length) {
      // The code below ensures we'll never go past the end of the array,
      // so we can assume this is an empty array
      return "[]"
    }

    // JSONify the value at idx
    json = jsonify( obj[idx] )

    if(idx < obj.length - 1) {
      // There are items left in the array, so increment the index and
      // JSONify the rest
      json = json + "," + jsonify( obj, idx + 1 )
    }

    // If this is the first item in the array, wrap the result in brackets
    if(idx === 0) { return "[" + json + "]" }

    return json
  }

  // Handle objects
  if(obj === Object(obj)) {
    var keys = Object.keys(obj)
    var key = keys[idx]

    // JSONify the key and value
    json = '"' + key + '":' + jsonify( obj[key] )

    if(idx < keys.length - 1) {
      // There are more keys, so increment the index and JSONify the rest
      return json + "," + jsonify( obj, idx + 1 )
    }

    // If this is the first key, wrap the result in curly braces
    if(idx === 0) { return "{" + json + "}" }

    return json
  }

  return obj.toString() // Naively handle everything else
}

var items = [ 9, "nine", { "key": [], "key2": { "subkey": 3.333 } } ]

console.log("OUTPUT", jsonify(items))
// => OUTPUT [9,"nine","key":[],"key2":{"subkey":3.333}]

There are a number of ways this could be tightened up (and I'm sure there are some bugs, too), but you get the idea.