Async & Performance Chapter 3, Promises Where does the async execution happen in a Promise?

[Cerebrum2]

The following code snippet is from Async & Performance Chapter 3.

I think the comment // start doing something that could take a while is misleading:

function foo(x) {
	// start doing something that could take a while

	// construct and return a promise
	return new Promise( function(resolve,reject){
		// eventually, call `resolve(..)` or `reject(..)`,
		// which are the resolution callbacks for
		// the promise.
	} );
}

If I understood correctly the async code should be inside the function passed to the Promise, no? So the following would be more accurate:

function foo(x) {
	// construct and return a promise
	return new Promise( function(resolve,reject){
                // start doing something that could take a while
                // then foo returns the newly created Promise
		// eventually, call `resolve(..)` or `reject(..)`,
		// which are the resolution callbacks for
		// the promise.
	} );
}

[Fov6363]

you are right;
function test_1() { console.log(1`);

return new Promise(function (resolve,reject) {
    console.log(`2`);

    return resolve(100);
})

}

test_1().then(val => console.log(val)); // 1 2 100`

[getify]

This is entirely valid and i've done it many times:

function foo() {
   ajax( "http://some. url", function(resp){
      resolve( resp );
   } );

   var resolve;

   return new Promise( function(res){
      resolve = res;
   } );
} 

[Cerebrum2]

@getify
Valid yes, but why not simplify?

function foo() {
   return new Promise( function(resolve){
       ajax( "http://some. url", resolve);
   } );
} 

[getify]

There are various reasons you want to "extract" the resolve capability as my snippet showed. I'm only pointing out that it's orthogonal/irrelevant how the actual promise resolving logic ends up getting handled.