Does the for loop block when the iteration invokes an async function without await keyword? (the inv-CodePudding

In the below pseudocode, when the for loop executes each iteration, then will the for loop block at each iteration waiting for the response of the async fetch (because await is used within the myasyncfn? Or do I need to use await keyword as shown in the comment below?

async myasyncfn(url){
return await fetch(url..).response;
}

for each url in url_array:
   myasyncfn(url);    #await myasyncfn(url)

CodePudding user response：

It will not wait for the async function to complete before continuing the loop; in that sense, it will block. However, that just means it iterates through all URLs in quick succession, firing many fetch requests, which will then all run in the background in parallel. Once the loop is done firing those, your thread is unblocked.

To illustrate:

async function foo(i) {
    await new Promise(resolve => setTimeout(resolve, 5000));
    console.log('Completed', i);
}

for (let i = 0; i < 10; i  ) {
    foo(i);
    console.log('Fired', i);
}

console.log('Done firing all async functions, unblocking...');