javascript - Will variables defined as undefined in JS occupy memory?

Question

let x = {
    'a' = 123
}

let y = {
    'a' = 123,
    'b' = undefined
}
let z = undefined;

如上，y会比x占用内存多么，z会占用内存么？

Answer 1

undefined occupies memory, has a fixed size, and is stored in the stack area, so z occupies memory. xy objects exist in the heap area, and their memory addresses are stored in stack memory. Because y has more undefined, it occupies more heap memory than x.