Array 2

.filter() #

Unlike map, it returns values from an array that match a specific criterion for each item.
It does not affect the original array, same as map().

 const numbers = [ 1 , 2 , 3 , 4];
const fruits = ['Apple' , 'Banana' , 'Cherry'];

const a = numbers.map(number => number < 3)
console.log(a); // [true ,true, false, false]

const b = numbers.filter(number => number < 3)
console.log(b); // [1,2]

console.log(numbers); // [ 1 , 2 , 3 , 4]

.find() , findIndex() #

find()
- Finds and returns an array element that matches a specific condition.
findIndex()
- Finds and returns an array element that matches a specific condition, and also returns its index.

const numbers = [ 1 , 2 , 3 , 4];
const fruits = ['Apple' , 'Banana' , 'Cherry'];

const a = fruits.find(fruit => {
  return /^B/.test(fruit) // '/^B/' is a regular expression. We'll look into this later. (For now, just know it means finding something that starts with B.)
})

console.log(a); // Banana

const b = fruits.findIndex(fruit => {
  return /^C/.test(fruit) 
})

console.log(b); // Cherry , 2

.includes() #

Returns a boolean indicating whether a specific value is included as an element in the array.

const numbers = [ 1 , 2 , 3 , 4];
const fruits = ['Apple' , 'Banana' , 'Cherry'];

const a = numbers.includes(3)
console.log(a) // true

const b = fruits.includes('Huemang');
console.log(b) // false

.push() .unpush() #

These methods modify the original array.

push(): Inserts a specific argument at the end of the array.
unshift(): Inserts a specific argument at the beginning of the array.

const numbers = [ 1 , 2 , 3 , 4];
const fruits = ['Apple' , 'Banana' , 'Cherry'];

numbers.push(5);
console.log(numbers) // [ 1 , 2 , 3 , 4 , 5 ]

numbers.unshift(0)
console.log(numbers) // [ 0 , 1 , 2 , 3 , 4 , 5 ]

.reverse() #

This method modifies the original array.
reverse means to turn something backward, and true to its name, it reverses the order of elements in an array.

const numbers = [ 1 , 2 , 3 , 4];
const fruits = ['Apple' , 'Banana' , 'Cherry'];

numbers.reverse();
fruits.reverse();

console.log(numbers) // 4 , 3 , 2 , 1
console.log(fruits) // 'Cherry' , 'Banana' , 'Apple'

.splice() #

This method modifies the original array.
Usage: splice(startIndex, deleteCount, itemsToAdd)
It's a method for deleting items from an array.
It can also insert items into an array.

const numbers = [ 1 , 2 , 3 , 4];
const fruits = ['Apple' , 'Banana' , 'Cherry'];

numbers.splice(2,1) // Delete 1 item starting from index 2.

console.log(numbers) // 1 , 2, 4

const numbers = [ 1 , 2 , 3 , 4];
const fruits = ['Apple' , 'Banana' , 'Cherry'];

numbers.splice(2,0,999) // Don't delete, just insert 999 at index 2.

console.log(numbers) // 1 , 2 , 999 , 3 , 4

Spread Operator #

It expands an array's data, outputting each item separated by commas.

Used by placing ... next to a variable.

const fruits = ['Apple' , 'Banana' , 'Cherry'];

console.log(...fruits)
// Apple Banana Cherry

function toObject(a,b,c){
  return {
    a: a,
    b: b,
    c: c
  }
}
console.log(toObject(...fruits))

Using the spread operator makes it easy to output items.
The spread operator can also be used in the parameter section, where it's called a rest parameter.