Simple javascript recursive function returns more values than actually exist?

Question

I am practicing recursion and have written this function:

var bigArray = ['a', ['b', ['c', ['d', {a:'e'}]]]];
var results = [];

function bagger293(bigArray){
  for (var item in bigArray){
    if (Array.isArray(bigArray[item])){
      bagger293(bigArray[item]);
    }
     else if (typeof bigArray[item] === 'object'){
      bagger293(bigArray[item]);
    }else{
      results.push(bigArray[item]);
    }
  }
}

bagger293(bigArray);
console.log(results);

I simply want the function to push any single value to an array, and search deeper if it is an object or array. Oddly, my function returns this:

[ 'a', 'b', 'c', 'd', 'e', 'd', 'e', 'c', 'd', 'e', 'd', 'e', 'b', 'c', 'd', 'e', 'd', 'e', 'c', 'd', 'e', 'd', 'e' ]

I assume it is because of my way of specifying

bigArray[item] but don't know why exactly.

expected result:

['a', 'b', 'c', 'd', 'e']

I don't even see how this is any good in context of recursion. — Quirk
– Quirk, Commented Oct 20, 2015 at 14:39

Paul Roub · Accepted Answer · 2015-10-20 14:41:39Z

4

You're missing an else. Once you've spotted an array, stop trying to do other things with it.

var bigArray = ['a', ['b', ['c', ['d', { a: 'e' }]]]];
var results = [];

function bagger293(bigArray) {
  for (var item in bigArray) {
    if (Array.isArray(bigArray[item])) {
      bagger293(bigArray[item]);
    } 
    else if (typeof bigArray[item] === 'object') {   // <--
      bagger293(bigArray[item]);
    } 
    else {
      results.push(bigArray[item]);
    }
  }
}

bagger293(bigArray);
console.log(results);

On the other hand, since all arrays are objects, you can just test for 'object':

var bigArray = ['a', ['b', ['c', ['d', { a: 'e' }]]]];
var results = [];

function bagger293(bigArray) {
  for (var item in bigArray) {
    if (typeof bigArray[item] === 'object') {
      bagger293(bigArray[item]);
    } 
    else {
      results.push(bigArray[item]);
    }
  }
}

bagger293(bigArray);
console.log(results);

edited Oct 20, 2015 at 14:41

answered Oct 20, 2015 at 14:41

Paul Roub

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1 Comment

Danmoreng Over a year ago

I was slightly faster. :o

Danmoreng · Accepted Answer · 2015-10-20 14:40:44Z

3

You are missing an else. Since an array is an object as well, your code starts the recursion twice.

This is working:

function bagger293(bigArray){
  for (var item in bigArray){
    if (Array.isArray(bigArray[item])){
      bagger293(bigArray[item]);
    }else if (typeof bigArray[item] === 'object'){
      bagger293(bigArray[item]);
    }else{
      results.push(bigArray[item]);
    }
  }
}

answered Oct 20, 2015 at 14:40

Danmoreng

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Comments

Oriol · Accepted Answer · 2015-10-20 14:44:57Z

2

All arrays are objects. No need to check both Array.isArray and typeof == 'object'.

var bigArray = ['a', ['b', ['c', ['d', {a:'e'}]]]];
var results = [];
(function bagger293(bigArray) {
  for (var item in bigArray)
    if (typeof bigArray[item] === 'object')
      bagger293(bigArray[item]);
    else
      results.push(bigArray[item]);
})(bigArray);
console.log(results);

answered Oct 20, 2015 at 14:44

Oriol

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