How is undefined treated in Binary in javascript?
It throws error when I do (undefined).toString(2).
But when I do
undefined & 0 //returns 0
undefined & 1 //returns 0
undefined | 0 //returns 0
undefined | 1 //returns 1
One might guess that undefined might be converted into 0 . Or Is there any other thing going ?
Kind of. When bitwise operators (and other operators which only make sense in terms of math - such as - and * and ** etc) are used, both expressions are converted into numbers first.
4. Let lnum be ? ToNumeric(lval).
5. Let rnum be ? ToNumeric(rval).
And ToNumeric does ToNumber which has
Argument Type Result
Undefined Return NaN.
And then the binary operators call ToInt32 on each operator, which has
- If number is NaN, +0𝔽, -0𝔽, +∞𝔽, or -∞𝔽, return +0𝔽.
So they're effectively converted into NaN in preparation for the mathematical operation, and then NaN gets converted to 0 for the binary operation.
(undefined).toString(2) doesn't work because accessing a property (like toString) of an expression only works if the expression is an object, or a primitive that can be wrapped in an object. Undefined and null are not objects, nor can they be converted into one, so trying to access any property of them throws.