How long does each function take to execute? ```javascript /** How long does each function take to execute */ function pause500ms () { return new Promise(res => setTimeout(res, 500)); } (async function test1 () { pause500ms(); pause500ms(); })(); (async function test2 () { await pause500ms(); await pause500ms(); })(); (async function test3 () { await Promise.all([pause500ms(), pause500ms()]); })(); (async function test4 () { await Promise.all([await pause500ms(), await pause500ms()]); })(); ```

Execution time of each function:

1. test1

(async function test1 () {
  pause500ms();
  pause500ms();
})();

Here, both pause500ms() functions are called, but their promises are not awaited (await is not used). This means the test1 function will finish almost instantly, not waiting for 500 ms. Execution time — approximately 0 ms.

2. test2

(async function test2 () {
  await pause500ms();
  await pause500ms();
})();

Here, calls are made sequentially: first waiting 500 ms for the first pause500ms(), then another 500 ms for the second. Total about 1000 ms.

3. test3

(async function test3 () {
  await Promise.all([pause500ms(), pause500ms()]);
})();

Both functions are started simultaneously, and we wait for both to finish. Since each takes 500 ms, total time — about 500 ms.

4. test4

(async function test4 () {
  await Promise.all([await pause500ms(), await pause500ms()]);
})();

Here, first await pause500ms() is executed, waiting 500 ms, then the second await pause500ms(), another 500 ms. As a result, Promise.all receives already completed values, and waiting is unnecessary. Total about 1000 ms.

Summary:

• test1: ~0 ms (does not wait)
• test2: ~1000 ms (sequentially)
• test3: ~500 ms (in parallel)
• test4: ~1000 ms (sequentially due to double await)

---

This behavior is related to the fact that await waits for the promise to resolve, and in test4, await inside the array causes sequential waiting, not parallel.