In below code, both c and c2 variables are awaiting for different promise instances and should run in serial but when run, the program completes in 100 miliseconds instead of 200.
function a1() {
return new Promise((x, y) => {
setTimeout(function () {
x(5);
}, 100);
});
}
async function run() {
let t1 = Date.now();
let b = a1();
let b2 = a1();
let c = await b;
let c2 = await b2;
console.log(Date.now() - t1);
}
run().then(function () {
console.log('@');
});Why is this behavior legal if await is defined as a serial operation?
You are calling a1() for both b and b2 when declaring them. Thus, by the time you await, the timeouts have already run and they each hold a promise, the await just resolves those promises.
If you want to see the full delay you should asign a1 to your b variables and then await the calls when declaring c, or simply await a1() twice.
let b = a1;
let b2 = a1;
let c = await b();
let c2 = await b2();
function a1() {
return new Promise((x, y) => {
setTimeout(function () {
x(5);
}, 100);
});
}
async function run() {
let t1 = Date.now();
let b = await a1();
let b2 = await a1();
console.log(Date.now() - t1);
}
run().then(function () {
console.log('@');
});