Wait in for loops for async function
I need run startFunc function synchronously and "wait" in for loop to finish task, to run it again. I can't use await in startFunc(). I need something like .wait() in c# I except result: start 1 end 1 start 2 end 2 etc...
function callToDB(ms) {
return new Promise(resolve => setTimeout(resolve, ms));
}
async function startFunc (i) {
console.log('start', i);
await callToDB(1000);
console.log('end', i);
}
for (let i = 0; i < 5; i++) {
startFunc(i);
}
Answers:
You need to put the for loop in an async function as well, so you can await each call to startFunc:
function callToDB(ms) {
return new Promise(resolve => setTimeout(resolve, ms));
}
async function startFunc (i) {
console.log('start', i);
await callToDB(1000);
console.log('end', i);
}
(async () => {
for (let i = 0; i < 5; i++) {
await startFunc(i);
}
})();Another method would be to continually chain .thens:
function callToDB(ms) {
return new Promise(resolve => setTimeout(resolve, ms));
}
async function startFunc (i) {
console.log('start', i);
await callToDB(1000);
console.log('end', i);
}
let prom = Promise.resolve();
for (let i = 0; i < 5; i++) {
prom = prom.then(() => startFunc(i));
}Or you could use .reduce and continually pass along the last Promise as the accumulator, rather than assign to an outside variable:
function callToDB(ms) {
return new Promise(resolve => setTimeout(resolve, ms));
}
async function startFunc (i) {
console.log('start', i);
await callToDB(1000);
console.log('end', i);
}
const finalProm = Array.from({ length: 5 })
.reduce(
(lastProm, _, i) => lastProm.then(() => startFunc(i)),
Promise.resolve()
);