replace for in with regular for loop with objects

Question

I'm currently trying to replace a for in loop that I have with a regular for loop out of curiosity, but with no success. I always get undefined. Is this even possible with javascript objects?

example object I loop over:

var el = {
    1: {type: "fish", commonName: "clownfish", scientificName: "sdasd", gender: "m", price: 1.99},
    2: {type: "fish", commonName: "dragonfish", scientificName: "dada", gender: "f", price: 2.99}
};

My working for in approach:

for (var element in el) {
   if (el[element].type === type && el.hasOwnProperty(element)) {
       elementNum++;
   }
}

The simple for loop approach that always gets me Cannot read property 'type' of undefined:

for(var i = 0, x = Object.keys(el).length; i < x; i++) {
   if (el[i].type === type && el.hasOwnProperty(i)) {
      elementNum++;
   }
}

@Matias has the right answer, but I'm wondering why you aren't using an array? Are some indexes going to be skipped or something? Also, switch the order of (el[i].type === type && el.hasOwnProperty(i)) so that it doesn't check for .type if el[i] doesn't exist (because javascript stops looking through the if AND statement if it finds one that is false. — Howzieky
– Howzieky, Commented Oct 30, 2016 at 20:23

Matías Fidemraizer · Accepted Answer · 2016-10-30 20:29:17Z

6

You're starting your loop from 0 while your first key in the whole object is 1.

var el = {
  1: {
    type: "fish",
    commonName: "clownfish",
    scientificName: "sdasd",
    gender: "m",
    price: 1.99
  },
  2: {
    type: "fish",
    commonName: "dragonfish",
    scientificName: "dada",
    gender: "f",
    price: 2.99
  }
};

var keyLength = Object.keys(el).length;

// I've simplified the for loop
for (var i = 1; i <= keyLength; i++) {
  console.log(el[i].commonName);
}

edited Oct 30, 2016 at 20:29

answered Oct 30, 2016 at 20:20

Matías Fidemraizer

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13 Comments

Tân Over a year ago

The answer cannot be shorter. Nice!

Sebsemillia Over a year ago

dammit, how could I not see this.. Thank you!!

Matías Fidemraizer Over a year ago

@Sebsemillia I would consider that sometimes my mind is like a language hint tool (JSHint, JSLint...) lol

Sebsemillia Over a year ago

@MatíasFidemraizer hehe ^^

rorymorris89 Over a year ago

Are there any benefits to this approach versus the original for (var element in el) { method?

|

Nina Scholz · Accepted Answer · 2016-10-30 20:31:57Z

0

I suggest to iterate directly over the keys of the object.

function getCount(type) {
    return Object.keys(el).reduce(function (r, k) {
        return r + +(el[k].type === type);
    }, 0);
}

var el = { 1: { type: "fish", commonName: "clownfish", scientificName: "sdasd", gender: "m", price: 1.99 }, 2: { type: "fish", commonName: "dragonfish", scientificName: "dada", gender: "f", price: 2.99 } };

console.log(getCount('fish'));

edited Oct 30, 2016 at 20:31

answered Oct 30, 2016 at 20:24

Nina Scholz

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2 Comments

Sebsemillia Over a year ago

yes, I know this approach as well. I just wanted to try to do it with a simple for loop.. ;) thank you for your answer!

Nina Scholz Over a year ago

it works only if the object is in a fixed notation for the keys, like indices.

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