Course: <https://www.executeprogram.com/courses/javascript-concurrency>

Overview

• complex callback
• Promises
• Async/wait
• Async programming: error handling, event scheduling

Summary

• Resolve promises with
  • Promise.resolve()
  • new Promise((resolve, reject) => {if() {resolve()} else {reject()}})
  • .then()
• nested promises get flattened (network requests write-read from disks)

Notes

• Everything is callbacks: JavaScript, promises, older async APIs like Node, network libraries, browser built-in APIs
• Concurrency: 2+ simultaneous events
• (to) instrument code with sth → attach measurement instrument to
  • instrument setTimeout with an arr
• delayed order for console.log(), arr.push()
• Execute console:
  • async console output / async result → always waits 3sec
  • console output / result → won't run setTimeout-callback

Synchronous

• runs all at once beginning-end

• .map() → result arr is fully constructed when returned

• Basic API of promises:

  function chain(value) {
    return {
      value: value,
      then: callback => {
        return chain(callback(value));
  }};}
  chain(5).then(n => n * 3); // returns 15
  chain(5); // returns {then: [function], value: 5} //Equal Promise.resolve(value)