Javascript patterns

Async Javascript patterns.js

Async Javascript Patterns!

async,await pattern.js

const myPromise = () => new Promise((resolve, reject) => {
  //...
  resolve(/*...*/);
  reject(/*...*/);
});

const soAsync = async () => {
  try {
    const myResult = await myPromise();
    const myResult2 = await myPromise(myResult);
    console.log('wow')
  } catch(error) {
    console.error('such reject');
  }
}

coroutine pattern.js

const P = require('bluebird');

const myPromise = () => new Promise((resolve, reject) => {
  //...
  resolve(/*...*/);
  reject(/*...*/);
});

const suchCoroutine = P.coroutine(function*(req, res){
  const someResult1 = yield myPromise(1);
  const someResult2 = yield myPromise(2);
  const someResult3 = yield myPromise(3);
  const someResult4 = yield myPromise(4);
  const someResult5 = yield myPromise(5);
  
  res.json({so: async})
})

coroutine with destructuring.js

const P = require('bluebird');

const myPromise = () => new Promise(resolve => {
  //...
  resolve({
    err: null, 
    resp: 'foo',
  });
});

const suchCoroutine = P.coroutine(function*(req, res) {
  
  const { err, resp } = yield myPromise(1);
  //... Assign to new variable names
  const { err: errorForThing, resp: thingResponse } = yield myPromise(resp);
  //... let's use different names!
  const { err, resp } = yield myPromise(errorForThing);  
  //... ES7: rest destructure:
  const { ...uberResponse } = yield myPromise(thingResponse);

  // lets use our uberResponse
  res.json({
    so: uberResponse.err,
    async: uberResponse.resp
  })
})

Pyramid of DOOM.js

// DO NOT DO THIS !
fs.readdir(source, function (err, files) {
  if (err) {
    console.log('Error finding files: ' + err)
  } else {
    files.forEach(function (filename, fileIndex) {
      console.log(filename)
      gm(source + filename).size(function (err, values) {
        if (err) {
          console.log('Error identifying file size: ' + err)
        } else {
          console.log(filename + ' : ' + values)
          aspect = (values.width / values.height)
          widths.forEach(function (width, widthIndex) {
            height = Math.round(width / aspect)
            console.log('resizing ' + filename + 'to ' + height + 'x' + height)
            this.resize(width, height).write(dest + 'w' + width + '_' + filename, function(err) {
              if (err) console.log('Error writing file: ' + err)
              fs.readFileSync(source + 'foobar.txt', function (err, file1) {
                // do something silly
                fs.readFileSync(source + 'foobar2.txt', function (err, file2) {
                  fs.readFileSync(source + 'foobar3.txt', function (err, file3) {
                      // SUCH MESS
                  })
                })
              })
            })
          }.bind(this))
        }
      })
    })
  }
})