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.