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:
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:
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.
0
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