Create a nested list from array

Question

This is the 3rd question from Eloquent JavaScript chapter 4.

Basically it wants me to create a function that will make an array into a nested list from array.

E.g. arrayToList([1, 2, 3]) should return:

var list = {
  value: 1,
  rest: {
    value: 2,
    rest: {
      value: 3,
      rest: null
    }
  }
};

I wonder why my code leads to an infinite loop.

function arrayToList(arr) {
  var list = {};
  for (var i = 0; i < arr.length; i++) {
    var a = arr[i];
    function add(res) {
      if (i == 0) {
        res.value = a;
        res.rest = "null";
      }
      else {
        i -= 1;
        add(res.rest);
      }
    }
    add(list);
  }
  return list;
}

Thank you for taking a look!

tymeJV · Accepted Answer · 2015-07-24 20:51:34Z

1

You subtract 1 for i in the middle of the loop if it's not 0 - so it never finishes the for - you can use recursion for this!

function addToList(obj, arr, index) {
    obj.value = arr[index];
    if (index == (arr.length - 1)) {
        obj.rest = null
    } else {
        obj.rest = {};
        addToList(obj.rest, arr, index + 1)
    }
}

var myObj = {}; 
var arr = [1,2,3];

addToList(myObj, arr, 0)

Demo: http://jsfiddle.net/freab275/

answered Jul 24, 2015 at 20:51

tymeJV

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Comments

dsh · Accepted Answer · 2015-07-24 20:50:01Z

0

You are playing games with your loop counter and the recursion. Each time i is not 0 you subtract one, then the loop adds one. So with one step back and one step forward you never finish. Add some print statements to see what i is each time you reference it.

answered Jul 24, 2015 at 20:50

dsh

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