Await `Promise.all()` vs. Multiple `await`: When to Use Which?

Await Promise.all() vs. Multiple Await

In asynchronous programming, deciding between using await Promise.all() and multiple await statements can influence execution timing and error handling. Here's a comparison of their key differences.

Example 1: Execution Timing

Using Promise.all() to concurrently execute tasks can result in faster completion than waiting for tasks sequentially:

let data = await Promise.all([task1(), task2(), task3()]);

// ms ------1---------2---------3---------4---------5
// =============================O task 1
// ====================O           task 2
// =========O                     task 3
//
// =============================O Promise.all

Example 2: Error Handling

Promise.all() behaves differently compared to multiple await statements when handling errors:

• Promise.all( [task1(), task2()] ): If any of the tasks in the array reject, the Promise.all() promise will reject immediately with an aggregate error object containing all the errors encountered.
• const t1 = task1(); const t2 = task2(); const r1 = await t1; const r2 = await t2;: If task1() rejects, execution will continue to the next line, where await t2; will be executed; if task2() also rejects, only that rejection will be passed on as an unhandled exception.

In summary, Promise.all() provides concurrent execution but fails early on any rejection, while multiple await statements execute tasks sequentially, allowing for individual error handling. Choose wisely based on the specific requirements of your application.

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