Array

Declaration

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

index position

const fruits = ["사과", "바나나"];
console.log(fruits);
console.log(fruits.length);
console.log(fruits[0]); //첫 인덱스
console.log(fruits[1]);
console.log(fruits[2]);
console.log(fruits[fruits.length - 1]); //마지막 인덱스

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Looping over an array

• print all fruits

1) for

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

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2) for..of

for (const fruitV of fruits) {
  console.log(fruitV);
}

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3) forEach(콜백함수)

fruits.forEach((value, index) => console.log(value, index));
console.log("---------------------------------");

fruits.forEach((value) => console.log(value));
console.log("===================================");

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Add, Delete

push

• add an item to the end

fruits.push("딸기", "복숭아");
console.log(fruits);

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pop

• remove an item from the end

fruits.pop();
console.log(fruits);
fruits.pop();
console.log(fruits);

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unshift

• add an item to the begining

fruits.unshift("키위", "레몬");
console.log(fruits);

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shift

• remove an item from the begining

fruits.shift();
console.log(fruits);
fruits.shift();
console.log(fruits);

• 📢주의!! : shift, unshift are slower than pop, push

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splice

• remove an item by index position

fruits.push("딸기", "복숭아", "레몬");
console.log(fruits);
fruits.splice(1, 1);
console.log(fruits);

fruits.splice(1, 1, "수박", "멜론");
console.log(fruits);

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concat

• combine two arrays

const fruits2 = ["배", "구아바"];
const newFruits = fruits.concat(fruits2);
console.log(newFruits);

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Searching

indexOf

• find the index

console.log(fruits);
console.log(fruits.indexOf("사과"));
console.log(fruits.indexOf("수박"));
console.log(fruits.indexOf("구아바"));	//없으면 -1

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includes

• 있는지 여부(true/false)

includes
console.log(fruits.includes("수박"));
console.log(fruits.includes("구아바"));

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lastIndexOf

• 끝에서부터

fruits.push("사과");
console.log(fruits);
console.log(fruits.indexOf("사과"));
console.log(fruits.lastIndexOf("사과"));