Coding Challenge Practice - Question 91

[MyrinNew]

The task is to implement the async function helper parallel()


The boilerplate code






function parallel(funcs){
// your code here
}







The parallel function is supposed to accept an array of async functions, run all the functions at the same time, with each function having the form func(callback).


If there are no functions






if (funcs.length === 0) {
callback(undefined, []);
return;
}







Store the outputs by index, count the finished tasks and ensure the callback fires only once






const results = [];
let completed = 0;
let hasError = false;







To run all the functions in parallel






funcs.forEach((func, index) => {
func((error, result) => {







To prevent multiple callbacks






if (hasError) return;







To handle errors






if (error) {
hasError = true;
callback(error, undefined);
return;
}







To preserve the order even if tasks finish out of order






results[index] = result;







The callback should be called when all the tasks are completed






completed++;

if (completed === funcs.length) {
callback(undefined, results);
}







The final code






function parallel(funcs){
// your code here
return function (callback) {
if(funcs.length === 0) {
callback(undefined, []);
return;
}

const results = [];
let completed = 0;
let hasError = false;

funcs.forEach((func, index) => {
func((error, result) => {
if(hasError) return;

if(error) {
hasError = true;
callback(error, undefined);
return;
}
results[index] = result;
completed++;

if (completed === funcs.length) {
callback(undefined, results)
}
})
})
}
}







That's all folks!




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