kingsubin

Array

 

1. Declaration

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

 

 

2. Index position

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

 

 

3. Looping over an array

• print all fruits

// 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, index) => console.log(fruit));

 

 

4. Addition, deletion, copy

// push: add an item to the end
fruits.push('berry', 'peach');
console.log(fruits); // 'apple', 'banana', 'berry', 'peach'

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

// unshift: add an item to the beginning
fruits.unshift('berry', 'remon');
console.log(fruits); //  'berry', 'remon', 'apple', 'banana'

// shift: remove an item to the beginning
fruits.shift();
fruits.shift();
console.log(fruits); // 'apple', 'banana'

// note!! shift, unshift are slower than pop, push

// splice: remove an item by Index position
fruits.push('berry', 'peach', 'remon');
console.log(fruits); // 'apple', 'banana', 'berry', 'peach', 'remon'
fruits.splice(1, 1); // 1부터 1개 지워줘
console.log(fruits); // 'apple', 'berry', 'peach', 'remon'
fruits.splice(1, 1, 'apple', 'watermelon'); // 1부터 1개 지우고 사과와 수박을 넣어줘
console.log(fruits); // 'apple','apple', 'watermelon' 'peach', 'remon'

// combine two arrays
const fruits2 = ['mango', 'coconut'];
const newFruits = fruits.concat(fruits2);
console.log(newFruits); // 'apple','apple','watermelon','peach','remon','mango','coconut'

 

 

5. Searching

// indexOf: find the index
console.log(fruits.indexOf('apple')); // 0
console.log(fruits.indexOf('watermelon')); // 2
console.log(fruits.indexOf('coconut')); // -1

// includes : 포함하고 있느가 ?
console.log(fruits.includes('apple')); // true
console.log(fruits.includes('king')); // false

// lastIndexOf : 제일 마지막에 있는거
console.log(fruits.lastIndexOf('apple')); // 1

 

 

 

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※출처

www.youtube.com/channel/UC_4u-bXaba7yrRz_6x6kb_w