Where we need promise
When the time of using javascipt code if there is delay in output for example if you are developing student management system with role number you need to access particular fees details but accessing roll number is time taking process in the case need to use promise
Promise definition
const delay = new Promise(resolve => {
setTimeout(() => {
resolve();
}, 90000);
});
Promise calling function
delay.then(()=> {
console.log("Done Waiting");
})
Promise in loop
const delays = [122, 100, 2000, 600];
const delay = (millisec) => {
return new Promise(resolve => {
setTimeout(() => {
console.log(millisec);
resolve(millisec)
}, millisec);
})
}
Promise.all(
delays.map(d => delay(d))
).then(() => { console.log("-----------") })
Ref : https://medium.com/developer-rants/running-promises-in-a-loop-sequentially-one-by-one-bd803181b283
https://stackoverflow.com/questions/65167410/wait-for-array-map-iterations-in-promise-all
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