[Javascript] avoid mutation: Array.prototype.toSpliced() vs splice()

Array.prototype.splice()mutates the original array. To avoid mutation, we use Array.prototype.slice().

new method Array.prototype.toSpliced() return a new array to avoid the mutation.

const months = ["Jan", "Mar", "Apr", "May"];

// Inserting an element at index 1
const months2 = months.toSpliced(1, 0, "Feb");
console.log(months2); // ["Jan", "Feb", "Mar", "Apr", "May"]

// Deleting two elements starting from index 2
const months3 = months2.toSpliced(2, 2);
console.log(months3); // ["Jan", "Feb", "May"]

// Replacing one element at index 1 with two new elements
const months4 = months3.toSpliced(1, 1, "Feb", "Mar");
console.log(months4); // ["Jan", "Feb", "Mar", "May"]

// Original array is not modified
console.log(months); // ["Jan", "Mar", "Apr", "May"]

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/toSpliced