Sorted Union help

1 
function uniteUnique(arr) {
  var args = Array.prototype.slice.call(arguments, 1);
  var newArr = [];
  if(args.length <= 2) {
   newArr = args[0].concat(args[1]);
  } else {
    newArr = args[0].concat(args[1], args[2]);
  }
   for(var i = 0; i < newArr.length; i++) {
    if(arr.indexOf(newArr[i]) !== -1) {
      delete newArr[i];
    }
  }
  newArr = newArr.filter(function(val){
    return val !== null;
  });
  return arr.concat(newArr);
}

uniteUnique([1, 2, 3], [5, 2, 1]);

Why is this test returning null as the final value? Shouldn’t the filter be getting rid of it?

2

When I ran the test, it gave me undefined as the final value rather than null. Have you tried making the filter return != undefined?

3

No. I will try it though.

4

It works thanks. Can you explain why I should test against undefined as well as null?

5

These are the seven built-in types in javascript: null, undefined, boolean, number, string, object, & symbol.

Null and undefined might seem the same but I believe the difference is that a value is set to null intentionally. That is, you the coder would set the value to null to indicate that the variable (or whatever) is intentionally blank.

6

In case you’re wondering, the reason you’re getting undefined in the first place is because of how you declared your args variable.
Array.prototype.slice.call(arguments, 1);
This tells javascript to:

  1. Create a new array
  2. Discard the first argument passed
  3. Place all the other arguments in that new array.

So when passed the arguments ([1, 2, 3], [5, 2, 1]), args becomes [[5, 2, 1]].

That means when you do this:
newArr = args[0].concat(args[1]);
You are concatenating [5,2,1] with a non-existent (undefined) value.

1 Like
7

I believe it is that null is an empty value, like a void, and undefined is when there is no assigned value at all.

var a; // returns undefined

No value was assigned. This is the case when you target non-exsting values.
null is : none of the above
undefined is: 404 Not Found

I was going to say this, but I had the feeling your second response was what he meant, and I didn’t understand the example this was from well enough.