[Java Script] ECMAScript 5 & 6

< JS ES5 version > 

- "use strict"

: with strict mode, we can't use undeclared variables 

 

- string index 

str[0] 

 

- string literal break up 

" hello" 

+ "hh" 

=> return hello hh 

 

- Able to use reserved words as property names 

 

- Array reduce(), reduceRight() : sum of all numbers in an array 

 

- Array every() : numbers.every(myFunction) 

: function myFunction(value) {

           return value > 18;

}

 

- Array indexOf(), lastIndexOf()

: lastIndexOf() works same as indexOf(), but searches from the end of the array.

 

-JSON.parse() : used to convert the text into a JS object 

 

- JSON.stringify() 

 

- Date.now() : same as getTime() on a Date Object 

- toISOString() : converts a Date object to a string, using the ISO standard format 

 

[ Property Getters and Setters ] 

- Object.defineProperty() 

 

[ E5 Object Methods ] 

Managing Objects 

- Accessing the prototype => Object.getPrototypeOf(object)

 

- ES5 allows trailing commas in object & array 

BUT not in JSON! 

 

 

< JS ES6 version > 

- let 

: allows to declare a variable with block scope 

 

- const 

: the value can't be changed

 

- Arrow Function 

: NO need for function, return keyword 

* NOT hoisted * = > MUST defined before they are used! 

 

Using const is safer, since a function expression is always a constant value.

 

- Spread(...) Operator 

: expands an iterable (like an array) into more elements 

 

- Javascript Maps 

: use an Object as a 'key'

 

- JavaScript Classes

: use the keyword class to a create a class. 

* always add a method named 'constructor()' 

 

[ Promise ]

:  동기화 관련 

- 비동기 처리가 아닌 동기 처리로만 코드를 실행한다면, 특정 로직의 실행이 끝날때까지 기다리고 실행해야 하므로 웹 어플리케이션을 실행하는데 많은 시간이 걸림 

 

- setTimeout()  : web API의 한 종류 

- jquery +  callback 함수 

=> callback 함수 : 데이터가 준비된 시점에서만 지정된 함수(동작)이 작동됨 

 

[ async, await ] 

 

 

 

 

 

 

 

 

reference : w3schools.com