concat arrays in javascript

Hello guys today i will show you how to use inbuilt concat array method in javascript. What...

What is concat method?

Concat is used to merge two or more arrays and it always returns a new array instead of modifying the original arrays.

Example - 1

const array1 = [1,2,3,4,5,6];
const array2 = ["A","B","C","D"];

const array1ToArray2 = array1.concat(array2)
const array2ToArray1 = array2.concat(array1)

console.log(array1ToArray2)
console.log(array2ToArray1)

Output -

[
 1, 2, 3, 4, 5,
 6, 'A', 'B', 'C', 'D'
]
[
 'A', 'B', 'C', 'D', 1,
 2, 3, 4, 5, 6
]

• As you can see we have merged two arrays, one in which we have merged array1 to array2 and second in which we have merged array2 in array1.

Example 2 -

const array1 = [1,2,3,4,5,6];
const array2d = [[1,2],[3,4],[[5,6],[7,8]]];

const array1To2dArray = array1.concat(array2d)

console.log(array1To2dArray);

Output -

[ 1, 2, 3, 4, 5, 6, [ 1, 2 ], [ 3, 4 ], [ [ 5, 6 ], [ 7, 8 ] ] ]

• We have merged array1 with a 2-d array.

Example 3 -

const array1 = [1,2,3,4,5,6];

const separateConcatening = array1.concat(7,8,9,"E","F",true,false,null,undefined,
[10,11,"G","H"],{name:"shubham",age:21},12.967)

console.log(separateConcatening)

Output-

[1,2,3,4,5,6,7,8,9,'E','F',true,false,null,undefined,
 10,11,'G','H',{ name: 'shubham', age: 21 },12.967
]

• Here we have concated array1 with seprate items of different data type like strings, numbers float, boolean,null,undefined,array,object.

Example - 4

const array1 = [1,2,3,4,5,6];
const array2 = ["A","B","C","D"];
const array2d = [[1,2],[3,4],[[5,6],[7,8]]];

const concatArray = (...args) => {
 return args.flat(Infinity)
}

console.log(concatArray([1,2,3,4],[5,6,7,8],array1,array2,array2d))

Output -

[
 1, 2, 3, 4, 5, 6, 7, 8,
 1, 2, 3, 4, 5, 6, 'A', 'B',
 'C', 'D', 1, 2, 3, 4, 5, 6,
 7, 8
]

• We have created an arrow function which accepts an argument as rest parameter so that we can pass any number of arrays to it.
• Then using the array flat() method we have flatten the those array which are 2-dimensional and the returned result will be a 1-d array.

Example - 5

const array1 = [1,2,3,4,5,6];

const array1ToArray1 = array1.concat(array1)

console.log(array1ToArray1)

Output -

[
 1, 2, 3, 4, 5,
 6, 1, 2, 3, 4,
 5, 6
]

• Here we have merged array1 with itself.

Example - 6

const array1 = [1,2,3,4,5,6];
const array2 = ["A","B","C","D"];
const array2d = [[1,2],[3,4],[[5,6],[7,8]]];

const array1ToMultiple = array1.concat(array1,array2,array2d)
console.log(array1ToMultiple)

Output -

[1,2,3,4,5,6,1,2,3,4,5,6,'A', 'B', 'C', 'D',[ 1, 2 ],
 [ 3, 4 ],
 [ [ 5, 6 ], [ 7, 8 ] ]]

We can also merge multiple arrays by passing them inside concat method.