Promisify based solution for lab 8.2 .
I have tried a promisify based solution to lab 8.2 .
Share with you.
Any additional advice is welcome.
Solution 1:
'use strict' const { promisify } = require('util') const print = (err, contents) => { if (err) console.error(err) else console.log(contents) } const opA = (cb) => { setTimeout(() => { cb(null, 'A') }, 500) } const opB = (cb) => { setTimeout(() => { cb(null, 'B') }, 250) } const opC = (cb) => { setTimeout(() => { cb(null, 'C') }, 125) } // solution 1 const printHelper = (contents) => print(null, contents) const pOpA = promisify(opA) const pOpB = promisify(opB) const pOpC = promisify(opC) pOpA() .then(printHelper) .then(() => pOpB()) .then(printHelper) .then(() => pOpC()) .then(printHelper)
Solution 2:
'use strict' const { promisify } = require('util') const print = (err, contents) => { if (err) console.error(err) else console.log(contents) } const opA = (cb) => { setTimeout(() => { cb(null, 'A') }, 500) } const opB = (cb) => { setTimeout(() => { cb(null, 'B') }, 250) } const opC = (cb) => { setTimeout(() => { cb(null, 'C') }, 125) } // solution 2 const pOpA = promisify(opA) const pOpB = promisify(opB) const pOpC = promisify(opC) const operate = async () => { print(null, await pOpA()) print(null, await pOpB()) print(null, await pOpC()) } operate()
Comments
-
Hi,
I followed the .then approach according to the training Promises (Cont.) chapter where we want to execute serial each function.
const contentA = promisify(opA)
const contentB = promisify(opB)
const contentC = promisify(opC)contentA()
.then((contents) => {
print(contents)
return contentB()
})
.then((contents) => {
print (contents)
return contentC()
})
.then(print)0 -
@ghortat said:
Hi,I followed the .then approach according to the training Promises (Cont.) chapter where we want to execute serial each function.
const contentA = promisify(opA)
const contentB = promisify(opB)
const contentC = promisify(opC)contentA()
.then((contents) => {
print(contents)
return contentB()
})
.then((contents) => {
print (contents)
return contentC()
})
.then(print)That looks similar as mine. I abstracted the print function into a printHelper to make the code compact.
0 -
@krave said:
@ghortat said:
Hi,I followed the .then approach according to the training Promises (Cont.) chapter where we want to execute serial each function.
const contentA = promisify(opA)
const contentB = promisify(opB)
const contentC = promisify(opC)contentA()
.then((contents) => {
print(contents)
return contentB()
})
.then((contents) => {
print (contents)
return contentC()
})
.then(print)That looks similar as mine. I abstracted the print function into a printHelper to make the code compact.
You actually don't need to abstract the print function
const { promisify } = require("util"); const print = (err, contents) => { if (err) console.error(err); else console.log(contents); }; const opA = (cb) => { setTimeout(() => { cb(null, "A"); }, 500); }; const opB = (cb) => { setTimeout(() => { cb(null, "B"); }, 250); }; const opC = (cb) => { setTimeout(() => { cb(null, "C"); }, 125); }; const opAProm = promisify(opA); const opBProm = promisify(opB); const opCProm = promisify(opC); opAProm() .then(print) .then(() => opBProm()) .then(print) .then(() => opCProm()) .then(print);
0 -
@nosvalds said:
@krave said:
@ghortat said:
Hi,I followed the .then approach according to the training Promises (Cont.) chapter where we want to execute serial each function.
const contentA = promisify(opA)
const contentB = promisify(opB)
const contentC = promisify(opC)contentA()
.then((contents) => {
print(contents)
return contentB()
})
.then((contents) => {
print (contents)
return contentC()
})
.then(print)That looks similar as mine. I abstracted the print function into a printHelper to make the code compact.
You actually don't need to abstract the print function
const { promisify } = require("util"); const print = (err, contents) => { if (err) console.error(err); else console.log(contents); }; const opA = (cb) => { setTimeout(() => { cb(null, "A"); }, 500); }; const opB = (cb) => { setTimeout(() => { cb(null, "B"); }, 250); }; const opC = (cb) => { setTimeout(() => { cb(null, "C"); }, 125); }; const opAProm = promisify(opA); const opBProm = promisify(opB); const opCProm = promisify(opC); opAProm() .then(print) .then(() => opBProm()) .then(print) .then(() => opCProm()) .then(print);
Hi, nosvalds
If you look close at the code and set a debugger in the print function. Run the code in debug mode and you will notice that the actual method which log out A, B, C is
console.error
.I believe the intention of this function is for whatever error occurs. Not the normal workflow. So I adjusted the handler.
1 -
Prefer async/await to .then and .catch because
- it allows for async stack traces (stack traces over multiple event loop ticks that trace the awaiting of promises in async functions)
- if you forget the .catch handler you end up with a unhandled rejection handler
- less code noise with async await + less chance of deep nesting
1 -
@davidmarkclements Thank you for your advices.
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