[JavaScript] 배열(Array)

1. 배열 선언
2. 인덱스
3. 배열의 모든 원소 방문하기
4. Push, pop, unshift, shift
5. Searching

 

1. 배열 선언

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

 

2. 인덱스

const fruits = ['🍎', '🍌'];
console.log(fruits);
console.log(fruits.length);
console.log(fruits[0]);
console.log(fruits[1]);
console.log(fruits[2]); // -> undefined
console.log(fruits[fruits.length -1 ]);

 

3. 배열의 모든 원소 방문하기

console.clear();

// (a). for
for (let i =0; i<fruits.length; i++){
    console.log(fruits[i]);
}

// (b). for..of
for (let fruit of fruits) {
    console.log(fruit);
}

// (c). forEach
fruits.forEach((fruit) => console.log(fruit));

 

4. Push, Pop, Unshift, Shift

// push: add an item to the end
fruits.push('🍓', '🍑');
console.log(fruits);

// pop: remove an item from the end
fruits.pop();
console.log(fruits);

// unshift: add an item to the begining
fruits.unshift('🍋');
console.log(fruits);

// shift: remove an item from the begining
fruits.shift();
console.log(fruits);

// 주의@! shift, unshift are *slower* than pop, push
// splice: remove an item by index position
fruits.push('🍐', '🍉', '🍒');
console.log(fruits);
fruits.splice(1, 1);
console.log(fruits);
fruits.splice(1, 1, '🍇', '🍍');
console.log(fruits);

// combine two arrays
const fruits2 = ['🍐', '🍅'];
const newFruits = fruits.concat(fruits2);
console.log(newFruits);

 

5. Searching

// find the index
console.clear();
console.log(fruits);
console.log(fruits.indexOf('🍎'));
console.log(fruits.indexOf('🍉'));
console.log(fruits.indexOf('🍍'));

// includes -> boolean
console.log(fruits.includes('🍉'));
console.log(fruits.includes('🥥'));

// lastIndexOf
console.clear();
fruits.push('🍎');
console.log(fruits);

console.log(fruits.indexOf('🍎'));
console.log(fruits.lastIndexOf('🍎'));