freeCodeCamp: Seek and Destroy Algorithm System Bug

Just went through, the thread, I think this should be closed as an edge case with the camper’s code. I agree detecting such code is costly, and adding any instructions will cause confusion to users.

Closing. Feel free to continue the discussion or re-open, but in my honest opinion, this should be left as it is.

One other solution I just found is to change the comparative operator from !== to != If you are not using a strict comparison operator it will work.

@parisclinkscales

I looked at your code, and this is the fix:

function seeker (value){
  return value !== this.valueOf(); // 'this' is an object, so you need to call valueOf method
}

function destroyer(arr) {
  var filtered = arguments[0];
  for (var i = 1;i < arr.length;i++){
    filtered = filtered.filter(seeker,arguments[i]);
    }
  return filtered;
  }

@systimotic @parisclinkscales @Bouncey This is an easy-to-read solution:

function destroyer(arr) {
  var args = [];
  for(var i in arguments) { // gets all arguments and save them for the callback
    args.push(arguments[i]);
  }

  function isEqual(element){ // when you create a new function, a new arguments object is created
    for (var j = 1; j < args.length; j++){
      if(element == args[j]){
        return false;
      }
    }
    return true;
  }

  return arr.filter(isEqual);       
}

And cleaner solution:

function destroyer(arr) {
  return arr.filter(function(value) {
    return !this.includes(value);
  }, Array.prototype.slice.call(arguments, 1));
}

I’ve delved into this issue a bit more. Going from @elisecode247’s and @kevcomedia’s findings, here’s what I found. The second argument of Array.prototype.filter is the optional thisArg. If you pass an object, it will set this inside the callback. Without 'use strict';, this can only be an object. If what’s passed as the thisArg isn’t an object, it will set this to an empty object. With 'use strict;', this is no longer forced to be an object. It can now be set to a number. My source is Elise’s MDN article, a bit further down. @Bouncey I think this issue can be closed, as it was a code problem (a difficult one though). I’d love to hear your thoughts though. Maybe the description should be altered in some way to make people aware of this problem.

I want to work on this.

Check this out. It turns out isequal changes arguments[i] into a Number object, so the value !== this means value is compared to an object, and so it always returns true.

So the campers test case is running twice?

I logged value and this in isEqual and that seemed fine.

@BKinahan as for your Result : ¯\_(ツ)_/¯ that’s just weird