Node.jsのPromiseを学ぶ

const myPromise = new Promise((resolve, reject) => {
  const success = true;

  if (success) {
    resolve('Operation was successful!');
  } else {
    reject('Something went wrong.');
  }
});

const myPromise = new Promise((resolve, reject) => {
  const success = true;

  if (success) {
    resolve('Operation was successful!');
  } else {
    reject('Something went wrong.');
  }
});

myPromise
  .then(result => {
    console.log(result); // This will run if the Promise is fulfilled
  })
  .catch(error => {
    console.error(error); // This will run if the Promise is rejected
  })
  .finally(() => {
    console.log('The promise has completed'); // This will run when the Promise is settled
  });

const { setTimeout: delay } = require('node:timers/promises');

const promise = delay(1000).then(() => 'First task completed');

promise
  .then(result => {
    console.log(result); // 'First task completed'
    return delay(1000).then(() => 'Second task completed'); // Return a second Promise
  })
  .then(result => {
    console.log(result); // 'Second task completed'
  })
  .catch(error => {
    console.error(error); // If any Promise is rejected, catch the error
  });

async function performTasks() {
  try {
    const result1 = await promise1;
    console.log(result1); // 'First task completed'

    const result2 = await promise2;
    console.log(result2); // 'Second task completed'
  } catch (error) {
    console.error(error); // Catches any rejection or error
  }
}

performTasks();

promise1
  .then(function (result1) {
    console.log(result1);
    return promise2;
  })
  .then(function (result2) {
    console.log(result2);
  })
  .catch(function (error) {
    console.log(error);
  });

import { setTimeout as delay } from 'node:timers/promises';

await delay(1000);

const fs = require('node:fs').promises;
// Or, you can import the promisified version directly:
// const fs = require('node:fs/promises');

async function readFile() {
  try {
    const data = await fs.readFile('example.txt', 'utf8');
    console.log(data);
  } catch (err) {
    console.error('Error reading file:', err);
  }
}

readFile();

const { setTimeout: delay } = require('node:timers/promises');

const fetchData1 = delay(1000).then(() => 'Data from API 1');
const fetchData2 = delay(2000).then(() => 'Data from API 2');

Promise.all([fetchData1, fetchData2])
  .then(results => {
    console.log(results); // ['Data from API 1', 'Data from API 2']
  })
  .catch(error => {
    console.error('Error:', error);
  });

const promise1 = Promise.resolve('Success');
const promise2 = Promise.reject('Failed');

Promise.allSettled([promise1, promise2]).then(results => {
  console.log(results);
  // [ { status: 'fulfilled', value: 'Success' }, { status: 'rejected', reason: 'Failed' } ]
});

const { setTimeout: delay } = require('node:timers/promises');

const task1 = delay(2000).then(() => 'Task 1 done');
const task2 = delay(1000).then(() => 'Task 2 done');

Promise.race([task1, task2]).then(result => {
  console.log(result); // 'Task 2 done' (since task2 finishes first)
});

const { setTimeout: delay } = require('node:timers/promises');

const api1 = delay(2000).then(() => 'API 1 success');
const api2 = delay(1000).then(() => 'API 2 success');
const api3 = delay(1500).then(() => 'API 3 success');

Promise.any([api1, api2, api3])
  .then(result => {
    console.log(result); // 'API 2 success' (since it resolves first)
  })
  .catch(error => {
    console.error('All promises rejected:', error);
  });

Promise.resolve('Resolved immediately').then(result => {
  console.log(result); // 'Resolved immediately'
});

function mightThrow() {
  if (Math.random() > 0.5) {
    throw new Error('Oops, something went wrong!');
  }
  return 'Success!';
}

Promise.try(mightThrow)
  .then(result => {
    console.log('Result:', result);
  })
  .catch(err => {
    console.error('Caught error:', err.message);
  });

const { promise, resolve, reject } = Promise.withResolvers();

setTimeout(() => {
  resolve('Resolved successfully!');
}, 1000);

promise.then(value => {
  console.log('Success:', value);
});

myPromise
  .then(result => console.log(result))
  .catch(error => console.error(error)) // Handles the rejection
  .finally(error => console.log('Promise completed')); // Runs regardless of promise resolution

async function performTask() {
  try {
    const result = await myPromise;
    console.log(result);
  } catch (error) {
    console.error(error); // Handles any errors
  } finally {
    // This code is executed regardless of failure
    console.log('performTask() completed');
  }
}

performTask();

queueMicrotask(() => {
  console.log('Microtask is executed');
});

console.log('Synchronous task is executed');

process.nextTick(() => {
  console.log('Next tick callback');
});

console.log('Synchronous task executed');

setImmediate(() => {
  console.log('Immediate callback');
});

console.log('Synchronous task executed');