为什么此表达式会导致“ReferenceError”？

Question

Why does incrementing the same thing behave differently when I reference it via a variable?

function f() {
    return {};
}

let x = {};
x++; // OK
(f())++ // ReferenceError

Answer 1

The difference is due to that when js is evaluating the expression it starts by checking if the left hand side is convertible to a number and by quirkyness an object is converted to Nan whereas a function is is not and js throws an exception when trying to convert it before it is evaluated. See also here: https://tc39.es/ecma262/multipage/ecmascript-language-expressions.html#sec-postfix-increment-operator

Answer 2

This whole code doesn't make any sense. You cannot increment a object.