How to clone array in ES6 ?

The spread operator in ES6 is used to clone an array, whereas the slice() method in JavaScript is an older way that provides 0 as the first argument. These methods create a new, independent array and copy all the elements of oldArray to the new one i.e. both these methods do a shallow copy of the original array. 

Syntax: 

// Older way
var clonedArray= oldArray.slice(0)    

// ES6 way: spread operator
var clonedArrayES6= [...oldArray]    

Example: This example uses the spread operator to copy an array.

javascript

// Cloning array using spread
// operator- ES6

const oldArray = ["dog1", "dog2", "dog3"];

const clonedArrayES6 = [...oldArray];

// ["dog1", "dog2", "dog3"]
console.log(clonedArrayES6);

Output

[ 'dog1', 'dog2', 'dog3' ]

Equality and sameness: Unlike the “=” operator, which creates a new variable that just points to the original array instead of copying its elements, the spread operator creates a new, cloned array, with different references but the same values. Hence “=” operator creates a deep copy of the original array but the spread operator does a shallow copy. The array created by the spread operator has the same value as that of the old array but, is not as same as the old array. 

Example: This example shows the use of the above-explained approach.

javascript

// Equality and sameness in cloning array

const oldArray = ["dog1", "dog2", "dog3"];

const clonedArrayES6 = [...oldArray];
const newArray = oldArray;

// False, i.e. shallow copy
console.log(clonedArrayES6 === oldArray)

// True, i.e. deep copy
console.log(newArray === oldArray)

Output

false
true

Note: All the above examples can be tested by typing them within the script tag of HTML or directly into the browser’s console.