8. 배열 제대로 알고 쓰자

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JavaScript === dynamically typed language → 여러 타입을 담을 수 가 있다!! ! 검색, 정렬, 삽입, 삭제 !!! (array map set list) 자료구조, 알고리즘을 써야 좋은지를 확인해야 한다!!! 동일한 타입의 배열을 넣는 것이 좋다!! 삭제도 가능하다!!

'use strict'

// 1. Declaration

const arr1 = new Array();
const arr2 = [1,2];

//2. Index position

const fruits  = ['apple', 'banana'];
console.log(fruits);
console.log(fruits.length);
console.log(fruits[0]);
console.log(fruits[1]);
console.log(fruits[fruits.length-1]);
console.log(fruits[-1]); //에러

console.clear();
// 3. Loopgin over an array
// print all fruits
// a. for
for (let i = 0; i<fruits.length; i++) {
    console.log(fruits[i]);
}
// b. for
for (let fruit of fruits) {
    console.log(fruit);
}

//c.for
fruits.forEach(function(fruit, index, array){
    console.log(fruit, index);
});//callback 함수를 불러옴!! 

//c-1.forEach
fruits.forEach((fruit) => console.log(fruit));
//callback 함수를 불러옴!! 

//4.Addition, deletion, copy
// add an item to the end
fruits.push('apple','orange');
console.log(fruits);// apple, banana, apple, orange
// pop : remove an item from the end

fruits.pop();
console.log(fruits); //apple, banana, apple

// unshift : add an item to the beginning
// shift : remove an item from the beginning

fruits.unshift('strawberry','lemon');
console.log(fruits); //strawberry, lemon, apple, banana, apple
fruits.shift();
fruits.shift();
console.log(fruits); //apple, banana, apple


//note!! shift, unshift are slower than pop, push -> stack이라 빼고 다시 넣어야함! 
//splice : remove an item by index position
console.clear();
const fruits2 = ['apple','strawbery','orange','lemon','banana','grape'];
console.log(fruits2);
//fruits2.splice(2); //0번째 부터 n개만 남음
//fruits2.splice(1,3); //1번쨰 인덱스부터 3개 삭제
fruits2.splice(1,1,'kiwi','peach');//1번째 인덱스 1개 삭제하고, 그자리에 삽입!
console.log(fruits2);
fruits2.splice(4);

//combine two arrays 
const fruits3 = ['watermelon','mango'];
const newFruits = fruits2.concat(fruits3);
console.log(newFruits); //합쳐짐

//5. Searching
// find the index

console.clear();
console.log(fruits2);
console.log(fruits2.indexOf('mango')); //없음
console.log(fruits2.indexOf('peach')); //2번쨰
console.log(fruits2.includes('mango')); //false 
console.log(fruits2.includes('kiwi'));  //true

//last
console.clear();
fruits2.push('apple');
console.log(fruits2);
console.log(fruits2.indexOf('apple')); //0
console.log(fruits2.lastIndexOf('apple')); //4 -> 뒤에서 찾는 거!!

 

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