safe .toJSON()

gistfile1.js

function toString (obj) {
  function _toString (i) {
    if (obj[i] === null) return 'null'
    if (typeof obj[i] === 'undefined') return 'undefined'
    if (obj[i].toString) return obj[i].toString()
    else return ''
  }
  return _toString
}

function eq (x, y) {
  if (Object.keys(x).toString() !== Object.keys(y).toString()) return false
  if (Object.keys(x).map(toString(x)).toString() !== 
      Object.keys(y).map(toString(y)).toString() ) return false
  return true
}

function getSafe (self, circular) {  
  if (typeof self === 'object' || typeof self === 'function') var safe = {}
  if (Array.isArray(self)) var safe = []

  if (!circular) circular = [self]
  
  var recurse = []

  Object.keys(self).forEach(function (i) {
    if (i === 'toJSON') return
    if (typeof self[i] !== 'object' && typeof self[i] !== 'function') return safe[i] = self[i]
    if (self[i] === null) return safe[i] = self[i]
    for (var x=0;x<circular.length;x++) {
      if (eq(circular[x], self[i])) return  
    }
    recurse.push(i)
  })
  for (var i=0;i<recurse.length;i++) {
    circular.push(self[recurse[i]])
    safe[recurse[i]] = getSafe(self[recurse[i]], circular)
  }
  
  return safe
}

function toJSON () {
  return getSafe(this)
}

// MyObject.prototype.toJSON = toJSON