CODEWITHSUNDEEP
javascript
photosynthesis
photosynthesis

Reputation: 2890

type coercion in JavaScript

I guess I kind of know the differences between == and === in JavaScript, it is that == will do type coercion when compare but === will not. I understand the following code will be true:

console.log(true == "1");

but when the code below is false?

console.log(true == "true");

Upvotes: 5

Views: 145

Answers (2)

BinaryProphet
BinaryProphet

Reputation: 11

The boolean operand is converted into a numeric value and strings are converted into a numeric value since one operand is a number.

We end up with 1 == NaN. If either of the operands is NaN, the equal operator always returns false.

Upvotes: 1

Oriol
Oriol

Reputation: 288100

When you loosely compare a boolean with a value of another type, the boolean is coerced into a number.

And when you compare a number and a string, the string is coerced into a number.

The full rules are explained in The Abstract Equality Comparison Algorithm

The process is like this:

true == "true" ─┐
                ├─ Number(true)   // 1
 1   == "true" ─┤
                ├─ Number("true") // NaN
 1   ==  NaN   ─┤
                ├─ // Comparing with `NaN` always produces `false`
   false       ─┘

Upvotes: 4

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