Use the Spread Operator to Evaluate Arrays In-Place

ES6: Use the Spread Operator to Evaluate Arrays In-Place
ES6 introduces the spread operator, which allows us to expand arrays and other expressions in places where multiple parameters or elements are expected.

The ES5 code below uses apply() to compute the maximum value in an array:

var arr = [6, 89, 3, 45];
var maximus = Math.max.apply(null, arr); // returns 89
We had to use Math.max.apply(null, arr) because Math.max(arr) returns NaN. Math.max() expects comma-separated arguments, but not an array.

The spread operator makes this syntax much better to read and maintain.

const arr = [6, 89, 3, 45];
const maximus = Math.max(...arr); // returns 89
...arr returns an unpacked array. In other words, it spreads the array.

However, the spread operator only works in-place, like in an argument to a function or in an array literal. The following code will not work:

const spreaded = ...arr; // will throw a syntax error

Copy all contents of arr1 into another array arr2 using the spread operator.