Getting a "Circular" added to my array in Javascript

Question

In the process of learning Javascript. I have written a code which goes through an array and adds them to res array. It will also go through the nested arrays and add them element by element to res. I have used recursion for this. But after each nested array finishes I am getting a Circular added to res. Unable to find where the problem is.

var res = ["oldarray"];

function findthis(xar){
  for(let n=0; n<xar.length; n++) {
    if(xar[n] instanceof Array) {
      res.push(findthis(xar[n]));
    } else {
      res.push(xar[n]);
    }
  }
  return res;
}

var d = ["z", 9, 2, ["r", "r", ["X","X","X","X"], "r"], "f", "x"];

console.log(findthis(d));

output this gives. when it should be an array without the added [Circular]

['oldarray', 'z', 9, 2, 'r', 'r', 'X', 'X', 'X', 'X', [Circular], 'r', [Circular], 'f', 'x']

then change res.push(findthis(xar[n])); to findthis(xar[n]); That's where you push the circular references. — Thomas
– Thomas, Commented Apr 15, 2020 at 12:43
Does this answer on SO help you define what [Circular] means, and why its getting printed for you? stackoverflow.com/questions/7923959/… — fluidguid
– fluidguid, Commented Apr 15, 2020 at 12:45

Mureinik · Accepted Answer · 2020-04-15 12:45:35Z

2

[Circular] is printed out when you try to print an array or an object that contains a reference to itself. Here, you're getting it because you push the result of findthis (which is res) into res itself. To fix this, just remove the call to push in that case:

function findthis(xar){
  for(let n=0; n<xar.length; n++) {
    if(xar[n] instanceof Array) {
      findthis(xar[n]); // Here! findthis already pushes to res, no need for another push
    } else {
      res.push(xar[n]);
    }
  }
  return res;
}

answered Apr 15, 2020 at 12:45

Mureinik

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1 Comment

amars Over a year ago

Nailed it. That makes complete sense now that you point it out.

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