Basic Array Operations (Methods)

const friends = ['Michael', 'Steven', 'Peter'];
friends.push('Jay');
console.log(friends);
// prints  ['Michael', 'Steven', 'Peter', 'Jay']

Add elements

const friends = ['Michael', 'Steven', 'Peter'];
const newLength = friends.push('Jay');
console.log(newLength);
// prints 4

friends.unshift('John');
console.log(friends);
// prints ['John', 'Michael', 'Steven', 'Peter', 'Jay']

unshift() method is used to add one or more elements to the beginning of the given array. This function increases the length of the existing array by the number of elements added to the array.

JavaScript Array unshift() Method - GeeksforGeeks

Remove elements

friends.pop(); // Remove the last element
friends.pop();
console.log(friends);
// prints ['John', 'Michael', 'Steven']

friends.pop(); // Remove the last element
const popped = friends.pop();
console.log(popped);
// prints Peter
console.log(friends);
// prints  ['John', 'Michael', 'Steven']

friends.shift(); // First
console.log(friends);
// prints ['Michael', 'Steven']

console.log(friends.indexOf('Steven'));
// prints 1

friends.push(23);
console.log(friends.includes('Steven')); // true
console.log(friends.includes('Bob')); // false
console.log(friends.includes('23')); //  false

23은 string이고 23은 number이기 때문에

false값이 나온거임

console.log(friends.includes(23)); // true

if (friends.includes('Steven')) {
    console.log('You have a friend called Steven');
}
// prints You have a friend called Steven