CODEWITHSUNDEEP
javascriptcomparisonconditional-statements
Akshendra Pratap
Akshendra Pratap

Reputation: 2040

What is !0 converted to when compared using == in JavaScript?

I was tring a few things in the console.

!5 is actually false
0 is a falsy value, so
0 == !5 is true

Okay, but when i tried this

!0 is true
5 is a truthy, so
5 == !0 should be true

But its not, the console says false. Why is this happening?

Upvotes: 0

Views: 63

Answers (1)

user1106925
user1106925

Reputation:

The reason the last line is false is that the == isn't a simple boolean conversion. It usually tries to convert operands with non-matching types down to a number.

So the 5 doesn't need conversion since it's already a number but !0, which is true, does. The value true gets converted to 1, so it doesn't equal 5.

You can infer from this that 1 == !0 will be true, and indeed it is.

This is detailed in the ES5 spec in the Abstract Equality Comparison Algorithm, step 7, which says of the comparison x == y:

If Type(y) is Boolean, return the result of the comparison x == ToNumber(y).

So the right-hand boolean is coerced to a number with ToNumber. In this case, ToNumber says:

The result is 1 if the argument is true.

Upvotes: 5

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