Code Challenge: Null and Undefined

Question

Hi there,

I am stuck at fixing the code in this code challenge.. Here is the question:

The identical() method is being called but the variables are not identical. See if you can fix the code.

Here is what the code provided in text editor:

var myUndefinedVariable;
    var myNullVariable = null;

    if(myNullVariable == myUndefinedVariable) {
        identical();
    }

Here is what I came up with:

var myUndefinedVariable;
    var myNullVariable = null;

    if(myNullVariable === myUndefinedVariable) {
        identical(null);
    } else {
                identical(null);
        }

And I received error message says null, so i changed my code to the following:

var myUndefinedVariable;
    var myNullVariable = null;

    if(myNullVariable === myUndefinedVariable) {
        identical();
    }

And I got correct this time....I am not sure how I got it right...by changing the "==" to "===" and not adding the "else" statement... Can someone explains why I getting this question right?

Answer 1 · 2014-04-05T18:55:39Z

April 5, 2014 6:55pm

You didn't need the else statement in the first place. The task was to call a function in case those two variables were equal. The function itself wasn't your concern, it was the comparison.

JavaScript does something called type coercion when you compare two variables with ==. It'll convert datatypes automatically so it can compare them. Both undefined and null are falsy values, they're treated as false when compared with ==.

The goal here was to avoid type coercion and check for true equality (when types also match), and that's what the === operator does. That's why the third example worked.

Answer 2 · 2014-04-05T18:24:55Z

April 5, 2014 6:24pm

I would assume the last works because in theory two items compared with == can technically be non identical. For example a floating point value of 2 and an int (fixed number) value of 2 would be considered identical when comparing with ==. The difference is when using === the two values being compared would have to be the same type (int and int, not double and int) and have the same value. So when comparing values a floating point 2 and a fixed number 2 would not be the same. Though Javascript does't explicitly set types, they do apply when using ===.

In relation to this challenge I think the following link will explain it better than myself. http://thecodeship.com/web-development/the-undefined-vs-null-pitfall-in-javascript/

Answer 3 · 2014-07-09T07:03:00Z

July 9, 2014 7:03am

I plugged the correct answer in the Javascript console tool on Chrome and it came back undefined instead of true so I'm not sure if that was the right answer or not. If anyone could follow up with any input it would be greatly appreciated.

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Lawrence Lee

Lawrence Lee

Code Challenge: Null and Undefined

3 Answers

Dino Paškvan

Dino Paškvan

Ricardo Hill-Henry

Ricardo Hill-Henry

Dino Paškvan

Dino Paškvan

John Crillo

John Crillo

Dino Paškvan

Dino Paškvan