회고

• 프로그래밍도 중요하지만 CS가 더 중요하다...
  • 그걸 알면서도 안해?!!, 시간 배분 잘하자..
• D3.js 재밌네...
• GitHub Pages에 userid.github.io로 static html 하나 올림...
  • 엄청 간편하다...
  • 개발자들의 개발자가 되어야 살아남는건가...

JavaScript💫

✨ How to use promises

• 총평
  • Modern JavaScript에서 asynchronous programming 하는데 있어서 Promise 모르면 사람이 아니므로... 기본개념을 잘 숙지하자.
  • IE도 돌아가시고... XMLHttpRequest와 callback hell을 피할 수 있는(Promise) 시대에 감사하자.
• Table of Contents
  • Overview
  • Using the fetch() API
  • Chanining promises
  • Catching erros
  • Promise terminology
  • Combining multiple promises
  • async and awiat
  • Conclusion
• Punchline phrase/keyword
  • pending, fullfilled, rejected, settled, resolved
  • A promise is an object returned by an asynchronous function, which represents the current state of the operation.
• Code Snippets

const fetchPromise = fetch('https://mdn.github.io/learning-area/javascript/apis/fetching-data/can-store/products.json');

fetchPromise
	.then(response => {
  		if (!response.ok) {
          	throw new Error(`HTTP error: ${response.status}`);
        }
  		return response.json();
	})
	.then(data => {
  		console.log(data[0].name);
	})
	.catch(error => {
  		console.log(`Could not get products: ${error}`);
	});

이것저것

• Callback function 이란
  • A callback function is a function passed into another function as an argument, which is then invoked inside the outer function to complete some kind of routine or action.
  • Callbakcs are often used to continue code execution after an asynchronous operatin has completed - these are called asynchronous callbacks. A good example is the callback functions execued inside a .then() block chained onto the end of a promise after that promise fulfills or rejects. This structure is used in many modern web APIs, such as fetch().
  • Synchronous callback example

  function greeting(name) {
    alert(`Hello, ${name}`);
  }

  function processUserInput(callback) {
    var name = prompt('Please enter your name.);
    callback(name);
  }

  processUserInput(greeting);