snippets.md

• Async/Await
  • Error handling
  • operation in parallel
• Craft your own promisify
• Create an array of N elements
• Get last n elements of an array

async-await

async function example() {
  const arrayOfFetchPromises = [
    fetch('1.txt'),
    fetch('2.txt'),
    fetch('3.txt')
  ];
  
  // Regular iterator
  for (const item of arrayOfFetchPromises) {
    console.log(item); // logs a promise
  }
  
  // Async iterator
  for await(const item of arrayOfFetchPromises) {
    console.log(item); // logs a response
  }
}

error-handling:

// do this
const data = await doSomething()
    .catch(e => console.error('Error when doingSomething', e.message));
if (!data) { /* Bail out somehow */ }

// not this
try {
  ...
} catch(err) {
  ...
}

async-in-parallel

await Promise.all([ doSomething(), doSomethingElse()]);

// or even like this
const fixturesPromise = fixtureModel.fetchAll()
const teamPromise = teamModel.fetch(teamId)

const fixtures = await fixturesPromise
const team = await teamPromise

craft-promisify

const promisify = foo =>
    new Promise((resolve, reject) => {
        foo((error, result) => {
            if (error) {
                reject(error);
            } else {
                resolve(result);
            }
        });
    });

export default promisify;

// usage
promisify(callback => asyncOperation({}, callback)).then(); 

create-array-filled-up-with-ele

Array.from({length: 20}, (val, key) => {
  return {
    a: 12,
    i: key // 1,2,3,4,5...20
  }
})

Last N elements of array

['a','b','c','d','e'].slice(-2); // ['d','e']