Recently I discovered that Array.prototype.forEach() function is not suitable for 'awaitable' functions. Let's have a look at an example.
const getAsyncData = (n) => {
return new Promise((resolve, reject) => {
setTimeout(() => resolve(n), 500)
})
};
const arr = [1,2,3,4,5];
//forEach example
(async () => {
let total = 0;
arr.forEach(async n => {
let res = await getAsyncData(n);
console.log(res);
total += res;
});
console.log('total = ' + total);
})();
I expected that forEach will await for every call of the getAsyncData() function so that to calculate total correctly, but surprisingly the result was different.
total = 01
2
3
4
5
Obviously, forEach ignores await keyword and quits immediately so total is not calculated.