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- ES6const oldArray = ["dog1", "dog2", "dog3"];const clonedArrayES6 = [...oldArray];// ["dog1", "dog2", "dog3"]console.log(clonedArrayES6); |
[ '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 arrayconst oldArray = ["dog1", "dog2", "dog3"];const clonedArrayES6 = [...oldArray];const newArray = oldArray;// False, i.e. shallow copyconsole.log(clonedArrayES6 === oldArray)// True, i.e. deep copyconsole.log(newArray === oldArray) |
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.
