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10

5

async function test() 
 (async () => 
 var a = await this.test1();
 var b = await this.test2(a);
 var c = await this.test3(b); 
 this.doThis(a,b,c); 
 )();

What does it mean to put methods (test1,test2,test3) inside async () => )()?
I find it faster than

async function test() 
 var a = await this.test1();
 var b = await this.test2(a);
 var c = await this.test3(b); 
 this.doThis(a,b,c); 

Any downside of using it?

javascript async-await

share|improve this question

edited Jul 12 at 20:20

Li357

36.2k88 gold badges7575 silver badges9999 bronze badges

asked Jul 12 at 20:04

bbusdriverbbusdriver

55911 gold badge55 silver badges2626 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  It just seems faster because the returned promise doesn't doesn't actually wait for any of your sequential logic. You might as well change it to a synchronous function since the returned promise is basically a return Promise.resolve(); in the first case, which isn't useful at all.
  
  – Patrick Roberts
  Jul 12 at 20:14
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  if it's not useful at all, when should one use (async () => )();?
  
  – bbusdriver
  Jul 12 at 20:36
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  At the top level, when you want access to async / await syntax. If that expression exists within another function, it means the caller of that function will not be able to know when the asynchronous calls have completed.
  
  – Patrick Roberts
  Jul 12 at 20:39
  

  
  
  
  

add a comment | 

10

5

async function test() 
 (async () => 
 var a = await this.test1();
 var b = await this.test2(a);
 var c = await this.test3(b); 
 this.doThis(a,b,c); 
 )();

What does it mean to put methods (test1,test2,test3) inside async () => )()?
I find it faster than

async function test() 
 var a = await this.test1();
 var b = await this.test2(a);
 var c = await this.test3(b); 
 this.doThis(a,b,c); 

Any downside of using it?

javascript async-await

share|improve this question

edited Jul 12 at 20:20

Li357

36.2k88 gold badges7575 silver badges9999 bronze badges

asked Jul 12 at 20:04

bbusdriverbbusdriver

55911 gold badge55 silver badges2626 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  It just seems faster because the returned promise doesn't doesn't actually wait for any of your sequential logic. You might as well change it to a synchronous function since the returned promise is basically a return Promise.resolve(); in the first case, which isn't useful at all.
  
  – Patrick Roberts
  Jul 12 at 20:14
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  if it's not useful at all, when should one use (async () => )();?
  
  – bbusdriver
  Jul 12 at 20:36
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  At the top level, when you want access to async / await syntax. If that expression exists within another function, it means the caller of that function will not be able to know when the asynchronous calls have completed.
  
  – Patrick Roberts
  Jul 12 at 20:39
  

  
  
  
  

add a comment | 

async function test() 
 (async () => 
 var a = await this.test1();
 var b = await this.test2(a);
 var c = await this.test3(b); 
 this.doThis(a,b,c); 
 )();

What does it mean to put methods (test1,test2,test3) inside async () => )()?
I find it faster than

async function test() 
 var a = await this.test1();
 var b = await this.test2(a);
 var c = await this.test3(b); 
 this.doThis(a,b,c); 

Any downside of using it?

javascript async-await

share|improve this question

edited Jul 12 at 20:20

Li357

36.2k88 gold badges7575 silver badges9999 bronze badges

asked Jul 12 at 20:04

bbusdriverbbusdriver

55911 gold badge55 silver badges2626 bronze badges

async function test() 
 (async () => 
 var a = await this.test1();
 var b = await this.test2(a);
 var c = await this.test3(b); 
 this.doThis(a,b,c); 
 )();

async function test() 
 var a = await this.test1();
 var b = await this.test2(a);
 var c = await this.test3(b); 
 this.doThis(a,b,c); 

share|improve this question

edited Jul 12 at 20:20

Li357

36.2k88 gold badges7575 silver badges9999 bronze badges

asked Jul 12 at 20:04

bbusdriverbbusdriver

55911 gold badge55 silver badges2626 bronze badges

share|improve this question

edited Jul 12 at 20:20

Li357

36.2k88 gold badges7575 silver badges9999 bronze badges

asked Jul 12 at 20:04

bbusdriverbbusdriver

55911 gold badge55 silver badges2626 bronze badges

edited Jul 12 at 20:20

Li357

36.2k88 gold badges7575 silver badges9999 bronze badges

edited Jul 12 at 20:20

Li357

36.2k88 gold badges7575 silver badges9999 bronze badges

asked Jul 12 at 20:04

bbusdriverbbusdriver

55911 gold badge55 silver badges2626 bronze badges

asked Jul 12 at 20:04

bbusdriverbbusdriver

55911 gold badge55 silver badges2626 bronze badges

1 Answer
1

active

oldest

votes

9

Both return a promise but they return different promises.

The first will return a promise that may resolve before this.test1()'s result resolves.

The second returns a promise that only resolves after the final call to this.doThis(a,b,c);.

This has been called the "fire and forget pattern":

Often in application development you want a process to call another thread and continue the process flow, without waiting for a response from the called thread. This pattern is called the “fire and forget” pattern.

You can see this in

function logEventually(str) 
 return new Promise((resolve) => 
 setTimeout(() => 
 console.log(str);
 resolve(null);
 , 0);
 );


async function a() 
 await logEventually('in a 1');
 await logEventually('in a 2');
 await logEventually('in a 3');
 return await logEventually('end of a');


async function b() 
 (async () => 
 await logEventually('in b 1');
 await logEventually('in b 2');
 await logEventually('in b 3');
 )();
 return await logEventually('end of b');


a();
b();

share|improve this answer

edited Jul 12 at 20:42

answered Jul 12 at 20:08

Mike SamuelMike Samuel

96.4k2424 gold badges175175 silver badges219219 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks. still not so sure when should one use (async () => )();
  
  – bbusdriver
  Jul 12 at 20:37
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  So if it resolves this.doThis(a,b,c); even before it resolves this.test1();, doesn't it mean that this.doThis(a,b,c); would error out?
  
  – bbusdriver
  Jul 12 at 20:40
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @bbusdriver I added a note about the "fire and forget" pattern. I think it fits what's going on in your example.
  
  – Mike Samuel
  Jul 12 at 20:42
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @MikeSamuel in regards to the "fire and forget" pattern, isn't the outer function generally synchronous? There's no reason for it to return a promise that doesn't actually wait for anything.
  
  – Patrick Roberts
  Jul 12 at 20:44
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @bbusdriver. The promise returned by the whole may resolve before test1 resolves. The chain of awaits within the inner lambda still proceed in the order implied by the await statements.
  
  – Mike Samuel
  Jul 12 at 20:45
  

  
  
  
  

 | 
show 3 more comments

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9

Both return a promise but they return different promises.

The first will return a promise that may resolve before this.test1()'s result resolves.

The second returns a promise that only resolves after the final call to this.doThis(a,b,c);.

This has been called the "fire and forget pattern":

Often in application development you want a process to call another thread and continue the process flow, without waiting for a response from the called thread. This pattern is called the “fire and forget” pattern.

You can see this in

function logEventually(str) 
 return new Promise((resolve) => 
 setTimeout(() => 
 console.log(str);
 resolve(null);
 , 0);
 );


async function a() 
 await logEventually('in a 1');
 await logEventually('in a 2');
 await logEventually('in a 3');
 return await logEventually('end of a');


async function b() 
 (async () => 
 await logEventually('in b 1');
 await logEventually('in b 2');
 await logEventually('in b 3');
 )();
 return await logEventually('end of b');


a();
b();

share|improve this answer

edited Jul 12 at 20:42

answered Jul 12 at 20:08

Mike SamuelMike Samuel

96.4k2424 gold badges175175 silver badges219219 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks. still not so sure when should one use (async () => )();
  
  – bbusdriver
  Jul 12 at 20:37
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  So if it resolves this.doThis(a,b,c); even before it resolves this.test1();, doesn't it mean that this.doThis(a,b,c); would error out?
  
  – bbusdriver
  Jul 12 at 20:40
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @bbusdriver I added a note about the "fire and forget" pattern. I think it fits what's going on in your example.
  
  – Mike Samuel
  Jul 12 at 20:42
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @MikeSamuel in regards to the "fire and forget" pattern, isn't the outer function generally synchronous? There's no reason for it to return a promise that doesn't actually wait for anything.
  
  – Patrick Roberts
  Jul 12 at 20:44
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @bbusdriver. The promise returned by the whole may resolve before test1 resolves. The chain of awaits within the inner lambda still proceed in the order implied by the await statements.
  
  – Mike Samuel
  Jul 12 at 20:45
  

  
  
  
  

 | 
show 3 more comments

9

Both return a promise but they return different promises.

The first will return a promise that may resolve before this.test1()'s result resolves.

The second returns a promise that only resolves after the final call to this.doThis(a,b,c);.

This has been called the "fire and forget pattern":

Often in application development you want a process to call another thread and continue the process flow, without waiting for a response from the called thread. This pattern is called the “fire and forget” pattern.

You can see this in

function logEventually(str) 
 return new Promise((resolve) => 
 setTimeout(() => 
 console.log(str);
 resolve(null);
 , 0);
 );


async function a() 
 await logEventually('in a 1');
 await logEventually('in a 2');
 await logEventually('in a 3');
 return await logEventually('end of a');


async function b() 
 (async () => 
 await logEventually('in b 1');
 await logEventually('in b 2');
 await logEventually('in b 3');
 )();
 return await logEventually('end of b');


a();
b();

share|improve this answer

edited Jul 12 at 20:42

answered Jul 12 at 20:08

Mike SamuelMike Samuel

96.4k2424 gold badges175175 silver badges219219 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks. still not so sure when should one use (async () => )();
  
  – bbusdriver
  Jul 12 at 20:37
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  So if it resolves this.doThis(a,b,c); even before it resolves this.test1();, doesn't it mean that this.doThis(a,b,c); would error out?
  
  – bbusdriver
  Jul 12 at 20:40
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @bbusdriver I added a note about the "fire and forget" pattern. I think it fits what's going on in your example.
  
  – Mike Samuel
  Jul 12 at 20:42
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @MikeSamuel in regards to the "fire and forget" pattern, isn't the outer function generally synchronous? There's no reason for it to return a promise that doesn't actually wait for anything.
  
  – Patrick Roberts
  Jul 12 at 20:44
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @bbusdriver. The promise returned by the whole may resolve before test1 resolves. The chain of awaits within the inner lambda still proceed in the order implied by the await statements.
  
  – Mike Samuel
  Jul 12 at 20:45
  

  
  
  
  

 | 
show 3 more comments

Both return a promise but they return different promises.

The first will return a promise that may resolve before this.test1()'s result resolves.

The second returns a promise that only resolves after the final call to this.doThis(a,b,c);.

This has been called the "fire and forget pattern":

Often in application development you want a process to call another thread and continue the process flow, without waiting for a response from the called thread. This pattern is called the “fire and forget” pattern.

You can see this in

function logEventually(str) 
 return new Promise((resolve) => 
 setTimeout(() => 
 console.log(str);
 resolve(null);
 , 0);
 );


async function a() 
 await logEventually('in a 1');
 await logEventually('in a 2');
 await logEventually('in a 3');
 return await logEventually('end of a');


async function b() 
 (async () => 
 await logEventually('in b 1');
 await logEventually('in b 2');
 await logEventually('in b 3');
 )();
 return await logEventually('end of b');


a();
b();

share|improve this answer

edited Jul 12 at 20:42

answered Jul 12 at 20:08

Mike SamuelMike Samuel

96.4k2424 gold badges175175 silver badges219219 bronze badges

function logEventually(str) 
 return new Promise((resolve) => 
 setTimeout(() => 
 console.log(str);
 resolve(null);
 , 0);
 );


async function a() 
 await logEventually('in a 1');
 await logEventually('in a 2');
 await logEventually('in a 3');
 return await logEventually('end of a');


async function b() 
 (async () => 
 await logEventually('in b 1');
 await logEventually('in b 2');
 await logEventually('in b 3');
 )();
 return await logEventually('end of b');


a();
b();

function logEventually(str) 
 return new Promise((resolve) => 
 setTimeout(() => 
 console.log(str);
 resolve(null);
 , 0);
 );


async function a() 
 await logEventually('in a 1');
 await logEventually('in a 2');
 await logEventually('in a 3');
 return await logEventually('end of a');


async function b() 
 (async () => 
 await logEventually('in b 1');
 await logEventually('in b 2');
 await logEventually('in b 3');
 )();
 return await logEventually('end of b');


a();
b();

function logEventually(str) 
 return new Promise((resolve) => 
 setTimeout(() => 
 console.log(str);
 resolve(null);
 , 0);
 );


async function a() 
 await logEventually('in a 1');
 await logEventually('in a 2');
 await logEventually('in a 3');
 return await logEventually('end of a');


async function b() 
 (async () => 
 await logEventually('in b 1');
 await logEventually('in b 2');
 await logEventually('in b 3');
 )();
 return await logEventually('end of b');


a();
b();

share|improve this answer

edited Jul 12 at 20:42

answered Jul 12 at 20:08

Mike SamuelMike Samuel

96.4k2424 gold badges175175 silver badges219219 bronze badges

answered Jul 12 at 20:08

Mike SamuelMike Samuel

96.4k2424 gold badges175175 silver badges219219 bronze badges

answered Jul 12 at 20:08

Mike SamuelMike Samuel

96.4k2424 gold badges175175 silver badges219219 bronze badges