问题
Say the code in a Promise constructor contains synchronous assignments. I have something like this:
function x() {
let rejector = null;
new Promise((resolve, reject) => {
rejector = reject;
// async code follows - setTimeout, network requests, etc.
});
return rejector;
}
Is the synchronous code in the Promise constructor guarunteed to execute, in this example, before the return statement of its containing function?
For me thus far it works every time — typeof x() == 'function' is always true; but I feel like I just happen to be winning a race. I ran it through a loop, 10^8 times, checking to see if I'd ever 'lose the race', but no, it was always successful. Does this always hold?
来源：https://stackoverflow.com/questions/59415313/is-the-promise-constructor-synchronous