Why doesn't this if statement work as expected?

Question

I came across with something like this today.(I thought that it would alert goodbye)

x = new Boolean(false);

if (x) {
  alert('hello');
}else{
    alert('goodbye');
}

I thought that was something like this(Which alerts goodbye):

x = false;

if (x) {
  alert('hello');
}else{
    alert('goodbye');
} 

I don't I understand how it works.

Answer 1

You should look up the "truthy - falsy" properties of javascript. Here is an article. In the first case x is true, because it is a non-null and non-undefined object, hence it is truthy. In the second, x is a boolean type of false, which is falsy.

Some things to remember from the article:

The following values are falsy:

• false
• 0 (zero)
• "" (empty string)
• null
• undefined
• NaN (a special Number value meaning Not-a-Number!)

Everything else is truthy!

Answer 2

If you use typeof x you realize x is an object. Object are always true.

Most values convert to true with the exception of the following, which convert to false:

• The empty string ""
• null
• undefined
• The number 0
• The number NaN
• The Boolean false

Answer 3

That's an instance of the Boolean function, not a boolean primitive.

true and false in javascript are boolean primitives. When you use them with boolean operators, they behave as you would expect. For example true || false is true and true && false is false.

On the other hand, Boolean is a special function which can convert other data types into boolean's (among other things). When you call new Boolean(false), you're creating a Boolean object which contains the boolean primitive false. That's the critical distinction in this case.

In short,

• if(new Boolean()) uses javascript's truthy value rules. It is an object which is not null, so it's "true".
• if(false) is a boolean primitive and actually checks for true/false.

Answer 4

new Boolean(false) returns an object which is not null. Non-null objects are always true.

reference