CODEWITHSUNDEEP
javascriptjsonrecursionjavascript-objects
Milos
Milos

Reputation: 1263

Using recursion to create a JSON string (replicate stringify)

I'm trying to replicate JSON.stringify() using recursion. I'm a bit confused as to why I'm getting undefined in my returned JSON string. Here's what I've done so far:

var testobj = {num:123,str:"This is a string",bool:true,o:{x:1,y:2},iamnull:null}
var count = 0
var stringifyJSON = function(obj) {

  // your code goes here
  if(obj === undefined){ 
  	return console.log("obj was undefined");
  }
  count = count + 1
  if(count > 20){  //I put this here mostly to stop infinite loops assuming this function wouldn't occur over 20 times.
  	return console.log("failed")
  }  
  var endarray = [];
if(obj !== undefined && typeof(obj)==='object'){  //If the object isn't undefined and the object is an object...

  for(var prop in obj){
   	console.log('"' + prop + '"');
  	endarray.push(stringifyJSON(prop) +'"' + ':' +'"'+ stringifyJSON(obj[prop])) //push the items into the array, using recursion. 
  }
  if(typeof(obj) !== undefined){
  	return '{' + endarray.join() + '}'
  }
}

  
  
};

//end result is "{undefined":"undefined,undefined":"undefined,undefined":"undefined,undefined":"{undefined":"undefined,undefined":"undefined},undefined":"{}}"

//JSON values cannot be a function, a date, or undefined

Could someone indicate where I'm going wrong? With recursion I'm having a problem identifying the source of the issue.

Upvotes: 0

Views: 2055

Answers (1)

Donovan McMurray
Donovan McMurray

Reputation: 199

There are a couple of things needed to get to the correct solution.

First, you don't have a base case for your recursion, so at the base level of each recursive trace, nothing is returned (i.e., undefined is implicitly returned). So first you must add a base case where ints, strings, booleans, and other primitive types, are converted to strings.

Second, you must also check that obj !== null before your recursive call, because typeof(null) evaluates to "object", strangely enough. 

var testobj = {num:123,str:"This is a string",bool:true,o:{x:1,y:2},iamnull:null}
var count = 0
var stringifyJSON = function(obj) {

  // your code goes here
  if(obj === undefined){ 
    return console.log("obj was undefined");
  }
  count = count + 1
  if(count > 20){  //I put this here mostly to stop infinite loops assuming this function wouldn't occur over 20 times.
    return console.log("failed")
  }  
  var endarray = [];
if(obj !== undefined && obj !== null && typeof(obj)==='object'){  //If the object isn't undefined and the object is an object...

  for(var prop in obj){
    console.log('"' + prop + '"');
    endarray.push(stringifyJSON(prop) +'"' + ':' +'"'+ stringifyJSON(obj[prop])) //push the items into the array, using recursion. 
  }
  if(typeof(obj) !== undefined){
    return '{' + endarray.join() + '}'
  }
}
if (obj !== undefined) {return String(obj)}


};

Upvotes: 1

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