Difference between normal for loop and for...in?

Question

I'm trying to write a function to fulfil the following requirements:

Given an object and a key, "getElementsThatEqual10AtProperty" returns an array containing all the elements of the array located at the given key that are equal to ten.

Notes:

If the array is empty, it should return an empty array.
If the array contains no elements are equal to 10, it should return an empty array.
If the property at the given key is not an array, it should return an empty array.
If there is no property at the key, it should return an empty array.

Example:

var obj = {
  key: [1000, 10, 50, 10]
};
var output = getElementsThatEqual10AtProperty(obj, 'key');
console.log(output); // --> [10, 10]

Approach #1 (fails the final point *If there is no property at the key, it should return an empty array.):

function getElementsThatEqual10AtProperty(obj, key) {

  var output = [];
  for (var i = 0; i < obj[key].length; i++) {
    if (obj[key][i] === 10) {
      output.push(obj[key][i]);
    }
  }
 return output;
}

Approach #2 passes all:

function getElementsThatEqual10AtProperty(obj, key) {

  var output = [];
  for (let i in obj[key]) {
    if (obj[key][i] === 10) {
      output.push(obj[key][i]);
    }
  }
  return output;
}

From my understanding, both loops and the subsequent conditional push has the same logic. Why does one work over the other?

https://stackoverflow.com/questions/5263847/javascript-loops-for-in-vs-for — epascarello, Dec 05 '17 at 04:00

score 1 · Answer 1 · answered Dec 05 '17 at 03:23

You're making this more complicated than it needs to be. I would just do this:

function getSameVals(yourArray, val){
  var a = [];
  for(var i=0,l=yourArray.length; i<l; i++){
    if(yourArray[i] === val){
      a.push(val);
    }
  }
  return a;
}
var ten = getSameVals(obj.key, 10);
console.log(ten);

Difference between normal for loop and for...in?

1 Answers1