JavaScript bitwise undefined pitfalls?
bit-manipulation, javascript, undefined, undefined-behavior
Solution
The internal function `[ToInt32]` is called on all operands for all bitwise operators.
Note that `ToInt32(undefined) -> 0` and the range is `[0, 2^32)`
Problem
What is the logic of bitwise operators on undefined??? ``` var x; console.log(x); // undefined console.log(x^7); // 7 console.log(7^x); // 7 console.log(x|7); // 7 console.log(7|x); // 7 console.log(7&x); // 0 console.log(x&7); // 0 console.log(~x); // -1 console.log(x*2); // NaN console.log(x/2); // NaN console.log(x+2); // NaN console.log(x-2); // NaN ``` I can see some sense in NaN. Because undefined -2 is really 'not a number'. But I do not follow any logic on bitwise operators and undefined.