How does a spread operator affect array splice

  • A+

I found the the following code and don't know what the difference between A and B is.

var fruits = ["Banana", "Orange", "Apple", "Mango"]; 


fruits.splice(2,0,["Lemon", "Kiwi"]); 


fruits.splice(...[2,0].concat(["Lemon", "Kiwi"])); 


First of all, Statement A & Statement B will generate different results.

In Statement A, you are inserting an array (["Lemon", "Kiwi"]) as an array element at position 2 while removing 0 items. So, you are inserting a string array in another string array at index 3.

var fruits = ["Banana", "Orange", "Apple", "Mango"];   fruits.splice(2,0,["Lemon", "Kiwi"]);  console.log(fruits);

However, Statement B is much more interesting. To, understand it fully first, log out it's core portion like this:

console.log(...[2,0].concat(["Lemon", "Kiwi"]));

As you can see it generates, 2 0 Lemon Kiwi. Then it is passed as parameter to fruits.splice( According to array#splice it will enter two strings (Lemon & Kiwi) at position 2, while removing 0 elements.

var fruits = ["Banana", "Orange", "Apple", "Mango"]; fruits.splice(...[2,0].concat(["Lemon", "Kiwi"]));  // is same as fruits.splice(2, 0, 'Lemon', 'Kiwi')  console.log(fruits);


  • array#splice updates the original array.
  • Statement A inserts an array in parent string array whereas, Statement B inserts two strings in parent string array.


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