Async Functions

refer to : https://www.udemy.com/course/the-web-developer-bootcamp/

A newer and cleaner syntax for working with async code! Syntax "makeup" for promise

• ASYNC
  • Async functions always return a promise
  • if the function returns a value, the promise will be resolved with that value
  • if the function throws an exception, the promise will be rejected.
  • 
• AWAIT

  We can only use the await keyword inside of functions declared with async

• await will pause the execution of the function, waiting for a promise to be resolved

• const login = async (username, password) => {
      if (!username || !password) throw 'Missing Credentials'
      if (password === 'corgifeetarecute') return 'WELCOME!'
      throw 'Invalid Password'
  }
  
  login('todd', 'corgifeetarecute')
      .then(msg => {
          console.log("LOGGED IN!")
          console.log(msg)
      })
      .catch(err => {
          console.log("ERROR!")
          console.log(err)
      })

  const delayedColorChange = (color, delay) => {
      return new Promise((resolve, reject) => {
          setTimeout(() => {
              document.body.style.backgroundColor = color;
              resolve();
          }, delay)
      })
  }
  
  async function rainbow() {
      await delayedColorChange('red', 1000)
      await delayedColorChange('orange', 1000)
      await delayedColorChange('yellow', 1000)
      await delayedColorChange('green', 1000)
      await delayedColorChange('blue', 1000)
      await delayedColorChange('indigo', 1000)
      await delayedColorChange('violet', 1000)
      return "ALL DONE!"
  }
  
  // rainbow().then(() => console.log("END OF RAINBOW!"))
  
  
  async function printRainbow() {
      await rainbow();
      console.log("END OF RAINBOW!")
  }
  
  printRainbow();

  const fakeRequest = (url) => {
      return new Promise((resolve, reject) => {
          const delay = Math.floor(Math.random() * (4500)) + 500;
          setTimeout(() => {
              if (delay > 2000) {
                  reject('Connection Timeout :(')
              } else {
                  resolve(`Here is your fake data from ${url}`)
              }
          }, delay)
      })
  }
  
  
  async function makeTwoRequests() {
      try {
          let data1 = await fakeRequest('/page1');
          console.log(data1);
          let data2 = await fakeRequest('/page2');
          console.log(data2);
      } catch (e) {
          console.log("CAUGHT AN ERROR!")
          console.log("error is:", e)
      }
  
  }

   try catch to handle errors in async functions