Chapter 10
Here are the solutions to the Exercises, for the Chapter 10, Keeping Your Promises chapter.
Exercise 1
No. Promise.race() will complete with the state of the first promise to complete. If the first resolves, then race() will resolve. If the first rejects, so will race().
Exercise 2
No. If any of the candidate promise rejects, then all() will reject. However, if no candidate promise has rejected, then all() will resolve when all candidate promises resolve.
Exercise 3
| | /* |
| | npm install fs-extra |
| | */ |
| | |
| | 'use strict'; |
| | |
| | const fs = require('fs-extra'); |
| | |
| | fs.readFile(__filename) |
| | .then(contents => console.log(contents.toString())) |
| | .catch(err => console.log(err.message)); |
Exercise 4
| | 'use strict'; |
| | |
| | const fs = require('fs-extra'); |
| | const request = require('request-promise'); |
| | |
| | const countPrimes = function(number) { |
| | if(isNaN(number)) { |
| | return Promise.reject(`'${number}' is not a number`); |
| | } |
| | |
| | return request(`http://localhost:8084?number=${number}`) |
| | .then(count => `Number of primes from 1 to ${number} is ${count}`); |
| | }; |
| | |
| | const createTimeout = function(timeInMillis) { |
| | return new Promise(function(resolve, reject) { |
| | setTimeout(() => reject(`timeout ${timeInMillis} MS`), timeInMillis); |
| | }); |
| | }; |
| | |
| | const logAndTerminate = function(err) { |
| | console.log(err); |
| | process.exit(1); |
| | }; |
| | |
| | const countPrimesForEachLine = function(pathToFile) { |
| | fs.readFile(pathToFile) |
| | .then(content => content.toString()) |
| | .then(content =>content.split('n')) |
| | .then(lines => Promise.race( |
| | [Promise.all(lines.map(countPrimes)), createTimeout(1000)])) |
| | .then(counts => console.log(counts)) |
| | .catch(logAndTerminate); |
| | }; |
| | |
| | countPrimesForEachLine('numbers.txt'); |
Exercise 5
| | 'use strict'; |
| | |
| | const fs = require('fs-extra'); |
| | const request = require('request-promise'); |
| | |
| | const countPrimes = function(number) { |
| | if(isNaN(number)) { |
| | return Promise.reject(`'${number}' is not a number`); |
| | } |
| | |
| | return request(`http://localhost:8084?number=${number}`) |
| | .then(count => `Number of primes from 1 to ${number} is ${count}`); |
| | }; |
| | |
| | const createTimeout = function(timeInMillis) { |
| | return new Promise(function(resolve, reject) { |
| | setTimeout(() => reject(`timeout ${timeInMillis} MS`), timeInMillis); |
| | }); |
| | }; |
| | |
| | const logAndTerminate = function(err) { |
| | console.log(err); |
| | process.exit(1); |
| | }; |
| | |
| | const readFileContents = function(pathToFile) { |
| | return fs.readFile(pathToFile) |
| | .then(content => content.toString()) |
| | .then(content =>content.split('n')); |
| | } |
| | |
| | const countPrimesForEachLine = async function(pathToFile) { |
| | try { |
| | const lines = await readFileContents(pathToFile); |
| | |
| | const counts = await Promise.race( |
| | [Promise.all(lines.map(countPrimes)), createTimeout(1000)]); |
| | |
| | console.log(counts); |
| | } catch(err) { |
| | logAndTerminate(err); |
| | } |
| | }; |
| | |
| | countPrimesForEachLine('numbers.txt'); |
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