Truthiness checker function in JavaScript

Question

I am going through this challenge on FCC and I am literally half way there!

Check if the predicate (second argument) is truthy on all elements of a collection (first argument).

function truthCheck(collection, pre) {
  // Is everyone being true?

  for(var i = 0; i < collection.length; i++){
    var arr = collection[i];
    for(pre in arr){
      if (isNaN(arr[pre]) ){
        pre = false;
        return pre;
      } else if (arr[pre]){
        pre = true;
        return pre;
      }
    }
  }
}

truthCheck([{"user": "Tinky-Winky", "sex": "male"}, {"user": "Dipsy", "sex": "male"}, {"user": "Laa-Laa", "sex": "female"}, {"user": "Po", "sex": "female"}], "sex");

In the introduction I said I was half way there. That's because when I evaluate the truthy values first:

if (arr[pre]){
  pre = true;
  return pre;
}

all the 'truthy' tests pass.

So I suppose I should be evaluated for 'truthtiness' in a different way? I say this because my code as is gets all the 'falsey' values to pass...

Thanks all!

Answer 1

It's false if falsey for any one of them, so test that. Then if none of them are falsey, return true.

function truthCheck(collection, pre) {
    for(var i = 0; i < collection.length; i++){
        if (!collection[i][pre]) { return false; }
    }
    return true;
}