I'm trying to create a promise-wrapper using generator so that I can do:

var asyncResult = PromiseWrapper( $.ajax( ... ) );

So far, I've been trying with:

function PromiseWrapper(promise){
    return function *wrapper(promise){
        promise.then(function(result){
            yield result;
        }, function(err){
            throw err;
        });
    }(promise).next().value
}

but this fails because yielding inside a normal is not allowed. Is there any work-around for this? Thank you :D

ps: I'm using babel to translate the code from es6 to es5

I'm trying to create a promise-wrapper using generator so that I can do:

var asyncResult = PromiseWrapper( $.ajax( ... ) );

So far, I've been trying with:

function PromiseWrapper(promise){
    return function *wrapper(promise){
        promise.then(function(result){
            yield result;
        }, function(err){
            throw err;
        });
    }(promise).next().value
}

but this fails because yielding inside a normal is not allowed. Is there any work-around for this? Thank you :D

ps: I'm using babel to translate the code from es6 to es5

• javascript
• generator
• ecmascript-6
• es6-promise

• yielding inside promise is not allowed - It should have been yielding inside a normal function is not allowed – thefourtheye Commented Apr 28, 2015 at 7:37
• @thefourtheye yep that's correct-- I'll edit it now – Dev Doomari Commented Apr 28, 2015 at 7:38

3 Answers 3

It is utterly impossible to wrap a promise in a generator that synchronously yields the promise's result, because promises are always asynchronous. There is no workaround for that, unless you throw mightier weapons like fibers at the asynchrony.

Would this approach work for you http://davidwalsh.name/async-generators ?

A modified example from the link:

function wrap(promise) {
    promise.then(function(result){
        it.next( result );
    }, function(err){
        throw err;
    });
}

function *main() {
    var result1 = yield wrap( $.ajax( ... ) );
    var data = JSON.parse( result1 );
}

var it = main();
it.next(); // get it all started

You should probably read the entirety of that post, the runGenerator is a pretty neat approach.

function step1(){

    return new Promise(function(c,e){
         setTimeout(function(){
              c(`1000 spet 1`);
         },1000)
    })

}

function step2(){
    return new Promise(function(c,e){
        setTimeout(function(){
            c(`100 spet 2`);
        },10000)
    })
}


function step3(){
    return new Promise(function(c,e){
        setTimeout(function(){
            c(`3000 spet 3`);
        },3000)
    })
}


function step4(){
    return new Promise(function(c,e){
        setTimeout(function(){
            c(`100 spet 4`);
        },100)
    })
}



function *main() {
    var ret = yield step1();
    try {
        ret = yield step2( ret );
    }
    catch (err) {
        ret = yield step2Failed( err );
    }
    ret = yield Promise.all( [
        step3( ret )

    ] );

    yield step4( ret );
}

var it = main();

/*
while (true) {
    var current = it.next();
    if (current.done) break;
    console.log(current.value);
}
*/
Promise.all( [ ...it ] ) // Convert iterator to an array or yielded promises.
    .then(
        function handleResolve( lines ) {

            for ( var line of lines ) {
                console.log( line );
            }
        })