FreeCodeCamp_JS_TIL_DAY3

0. use destructuring assignment to extract values from objects.

: neatly assigning values taken directly from an object.

1. use destructuring assignment to assign values from objects.

: allows you to assign a new variable name when extracting values.
 do this by putting the name after a colon when assigning the value.

const user = {name:'sam lee', age:30};

const {name:userName, age:userAge} = user;

// user.name = userName 이름의 변수로 저장됨.
//user.age = userAge이름의 변수로 저장됨.

console.log(userName) //sam lee출력
console.log(userAge) // 30출력

 

2. use destructuring assignment to assign variables from nested objects.

cosnt user = {
samlee : {
 age: 30,
 email: 'samlee@gmail.com'
 }
};

const {samlee: {age, email}} = user;
const {samlee:{samAge, samEmail}} = user;

 

3. use destructuring assignment to assign variables from arrays.

-> one key difference between the spread operator and array destructing is that the spread operator unpacks all contents of an array into a comma-separated list. 
-> consequently, you cannot pick of choose which elements you want to assign to variables.

 

 

4. use destructuring assignment with the rest parameter to reassign array elements.

*** the rest parameter only works correctly as the last variable in the list.
*** as in, you cannot use the rest parameter to catch a subarray that leaves out the last element of the original array.

const source = [1,2,3,4,5,6,7,8,9,10];

function removeFirstTwo(list) {
const [,,...arr] = list ;
return arr;
}
const arr = removeFirstTwo(source);

 

5. use destructuring assignment to pass an object as a Function's parameters

-> can destructure the object in a function argument itself.

#예제 (이해x)

freeCodeCamp.org

---

6. create strings using template literals

: 백틱 ``을 사용함.
-> allow you to create multi-line strings and to use string interpolation(내삽법) features to create strings.

`Hello my name is ${variable}! Nice to meet you`;

+ you can include other expressions in your string literal, ex) ${a + b}.

 

7. write concise object literal declarations using object property shorthand.

const getMousePosition = (x, y) => ({
  x: x,
  y: y
});

// is same as below

const getMousePosition = (x, y) => ({ x, y });

8. write concise declarative functions