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NodeJS Bluebird Promises

Converting nodeback library to Promises


const Promise = require('bluebird'),
 fs = require('fs')
Promise.promisifyAll(fs)
// now you can use promise based methods on 'fs' with the Async suffix
fs.readFileAsync('file.txt').then(contents => {
 console.log(contents)
}).catch(err => {
 console.error('error reading', err)
})

Functional Promises


Example of map:

Promise.resolve([ 1, 2, 3 ]).map(el => {
 return Promise.resolve(el * el) // return some async operation in real world
})

Example of filter:

Promise.resolve([ 1, 2, 3 ]).filter(el => {
 return Promise.resolve(el % 2 === 0) // return some async operation in real world
}).then(console.log)

Example of reduce:

Promise.resolve([ 1, 2, 3 ]).reduce((prev, curr) => {
 return Promise.resolve(prev + curr) // return some async operation in real world
}).then(console.log)

Coroutines (Generators)


const promiseReturningFunction = Promise.coroutine(function* (file) {
 const data = yield fs.readFileAsync(file) // this returns a Promise and resolves to the file
contents
 return data.toString().toUpperCase()
})
promiseReturningFunction('file.txt').then(console.log)



Conclusion

In this page (written and validated by ) you learned about NodeJS Bluebird Promises . What's Next? If you are interested in completing NodeJS tutorial, your next topic will be learning about: NodeJS Async Await.



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