Promises-sample-code

Essential for asynchronous programming Promises are vital for abstract a synchronous behaviour for your functions. The sample codes are simple examples of

• non-blocking execution
• functions
• callbacks
• promises nesting and changing
• async await.

Getting Started

I recommend to run the samples using Nodejs, you can install it following the link bellow:

Node.js - The official Nodejs website

1-non-blocking.js

console.log('Starting up')
setTimeout(() => {
console.log('Two seconds!')
}, 2000)
setTimeout(() => {
console.log('Zero seconds!')
}, 0)
console.log('Finishing up')

2-callbacks.js

const doWorkCallback = (callback) => {
setTimeout(() => {
callback('This is an error!', undefined)
//callback(undefined, [1,2,3])
},2000)
}
doWorkCallback((error, result) => {
if(error) {
return console.log(error)
}
console.log(result)
})

3-promises.js

const doWorkPromise = new Promise((resolve, reject) =>{
setTimeout(() => {
resolve([1,2,3])
// reject('This is an error!')
}, 2000)
})
doWorkPromise.then((result) => {
console.log('Success!', result)
}).catch((error) => {
console.log(error)
})

4-promises-nesting.js

const add = (a, b) => {
return new Promise((resolve, reject) => {
setTimeout(() => {
resolve(a + b)
}, 2000)
})
}
add(1, 2).then((sum) => {
console.log(sum)
add(sum, 7).then((sum2) => {
console.log(sum2)
add(sum2, 11).then((sum3) => {
console.log(sum3)
}).catch((error) => {
console.log(error)
})
}).catch((error) => {
console.log(error)
})
}).catch((error) => {
console.log(error)
})

5-promises-chaining.js

const add = (a, b) => {
return new Promise((resolve, reject) => {
setTimeout(() => {
resolve(a + b)
}, 2000)
})
}
add(1, 2).then((sum) => {
console.log(sum)
add(sum, 7).then((sum2) => {
console.log(sum2)
add(sum2, 11).then((sum3) => {
console.log(sum3)
})
})
}).catch((error) => {
console.log(error)
})

6-promises-async-await.js

const add = async (a, b) => {
return new Promise((resolve, reject) => {
setTimeout(() => {
if (a < 0 || b < 0) {
return reject('Numbers must be positive!')
}
resolve(a + b)
}, 2000)
})
}
const callAdd = async () => {
//Behaivour looks simple as synchronous function
const sum = await add(1, 99)
const sum1 = await add(sum, 12)
const sum2 = await add(sum1, 7)
return sum2
}
callAdd().then((result) => {
console.log(result)
}).catch((error) => {
console.log(error)
})

Authors

• Woltter Xavier - Initial work - GitHub Profile