An array is an object that can store multiple values at once.

What is the difference between non-constant array and const array variable?

Non-const array variable can initialize with whole new array also we can change the values.

let myarray = new Array();
myarray.push('value'); // Allowed
myarray = new Array(); // Allowed

Const array variable cannot be initialize again after declaration, only initilize at the time of declaration but we can change the values;

const myarray = new Array();
myarray.push('value'); // Allowed
myarray = new Array(); // It will throw exception

Different ways to create array

1. Using Array literal

let students = ['Ram', 'Sham', 'Gagan']; //Array with values
let studentsEmpty = []; //Empty array

// Objects array
let objArray = [
    {
        name: 'Rohit',
        age: '27'
    },
    {
        marks: 99,
        result: 'pass'
    }
];

1. Using New keyword

   let students = new Array();
   

2. Using Array constructor

   let students = new Array('Ram', 'Sham', 'Gagan');
   

   Array Methods

concat()

The concat() method is use to append the another array to current array

let students1 = ['Ram', 'Sham'];
let students2 = ['Sadan', 'Mahatre'];

// contact two arrays 
let concatStudents = students1.concat(students2);

console.info(concatStudents);
//output:: [Ram,Sham,Sadan,Mahatre]

concatStudents = students2.concat(students1);

console.info(concatStudents);
//output:: [Sadan,Mahatre,Ram,Sham]

console.info(['Sham', 'Ganga'].concat(['Radha', 'Maya']));
//output:: ['Sham', 'Ganga', 'Radha', 'Maya']

copywithin()

Syntax

```
array.copyWithin(target, start, end)
```

Parameters

• target - The position where the copied element takes place.
• start - It is optional. It represents the index from where the method starts copying elements. By default, it is 0.
• end - It is optional. It represents the index at which elements stops copying. By default, it is array.length-1.

Example

let studentsArray = ['rohit', 'sagar', 'kamala'];
let result = studentsArray.copyWithin(0,1,2);

console.info(result);
//output: ['sagar', 'sagar', 'kamala']

entries()

The entries() method creates a new iterator object of an array, holding the key/value pairs for every value in the array. A key represents the index number carrying an item as its value. It does not affect the original array.

Example 1

let colors = ['yellow', 'green', 'orange', 'black'];
newColors = colors.entries();

for(let color of newColors){
    console.info(color);
}

output

[0, 'yellow']
[1, 'green']
[2, 'orange']
[3, 'black']

Example 2

let colors = ['yellow', 'green', 'orange', 'black'];

let newColors = colors.entries();

for(let color of newColors){
    color.forEach((element) => {
        console.info(element);
    });
}

output

0
yellow
1
green
2
orange
3
black

pop()

Get last element and remove from the array

let colors = ['red', 'yellow', 'green'];

console.log(colors.pop());

//output: green

console.log(colors);
//output: ['red', 'yellow']

push()

Add new element at the end of the array

let colors = ['red', 'yellow', 'green'];

colors.push('black');

console.log(colors);
//output: ['red', 'yellow', 'green', 'black']

reverse()

To reverse elements order of the array

let colors = ['red', 'yellow', 'green'];

colors.reverse();

console.log(colors);
//output: ['green', 'yellow', 'red']

shift()

The JavaScript array shift() method removes the first element of the given array and returns that element. This method changes the length of the original array.

let colors = ['red', 'yellow', 'green'];

let color = colors.shift();

console.log(color);
//output: red

console.log(colors);
//output: ['yellow', 'green']

slice()

The JavaScript array slice() method extracts the part of the given array and returns it. This method doesn't change the original array.

let colors = ['red', 'yellow', 'green'];

let colorsSlice = colors.slice(1,3);

console.log(colorsSlice);
//output: ['yellow', 'green']

sort()

Sort method arrange elements in sorted order

let colors = ['red', 'yellow', 'green'];

let sortedColors = colors.sort();

console.log(sortedColors);
//output: ['green', 'red', 'yellow']

console.log(colors)
//output: ['green', 'red', 'yellow']

toString()

Converts array into command seprated string

let colors = ['red', 'yellow', 'green'];

console.log(colors.toString());

//output: red,yellow,green

unshift()

The JavaScript array unshift() method adds one or more elements in the beginning of the given array and returns the updated array. This method changes the length of the original array.

let colors = ['red', 'yellow', 'green'];

let count = colors.unshift('black')

console.log(colors);
//output: ['green', 'red', 'yellow']

console.log(count);
//output: 4