Adding async function to async waterfall

Question

I'm trying to develop a NodeJS app, but it wont executing as desired. I want to first execute downloadIMG first and then execute featureMatching and continue this until the for loop terminates. Guide me to rewrite the code in proper manner.

for (var i=0; i<dbImgCount; i++) {
    (function(i) {
        async.waterfall([
            async function downloadIMG(done) {
                try {
                    var options = {
                        url:  FolderPath[i].FolderPath,
                        dest: '/home/ubuntu/imgCompare/'                
                    }
                    const { filename, image } =  await download.image(options);
                    image2 = 'image.jpg';
                    done(null, 'hi');
                } catch (e) {
                    console.error(e)
                }
            },
            async function featureMatching(a, done){
                const img1 = cv.imread(image1);
                const img = 'image.jpg';
                const img2 = cv.imread(img);
                const orbMatchesImg = matchFeatures({
                    img1,
                    img2,
                    detector: new cv.ORBDetector(),
                    matchFunc: cv.matchBruteForceHamming
                    },
                    (console.log(image1+','+img))
                );
                done(null);
            }
        ],
        function (err) {});
    })(i);
}

George T Kurian · Accepted Answer · 2018-07-26 06:25:52Z

8

Got the answer from here. Async functions can be used in async waterfall by returning args as array from async function.

Like this

  async.waterfall([
           // ...
         async function (arg1, arg2) {
          //...
             const arg3 = await foo()

             return [arg1, arg2, arg3] //USE THIS, OTHERWISE 2ND fn WON'T WORK
         },
         function ([arg1, arg2, arg3], callback) {
           //...
         }
  ],function (err) {});

edited Jul 26, 2018 at 6:25

answered Jul 25, 2018 at 14:08

George T Kurian

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4 Comments

slebetman Over a year ago

There's a simpler, more elegant way. Async functions are promises. Async.js deal with callbacks, not promises. Use async-q instead which is designed for promises: npmjs.com/package/async-q

k0pernikus Over a year ago

Avoid link only anwers as those can go away at any time. Rather, add the relevant part from the linked source within your answer.

George T Kurian Over a year ago

@k0pernikus Hey, I mentioned relevant part of the answer in my comment!

Ralph Over a year ago

Try to use the new async/await... If you are investing your time in nodejs, better learn those, they will make things much easier. No need to use libraries such as async anymore.

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