en.javascript.info/1-js/4-data-structures/7-array/4-random-from-array/solution.md

We need to generate a random integer value from 0 to arr.length-1, and then take the element with that index.

Here we go:

let arr = ["Apple", "Orange", "Pear", "Lemon"];

let rand = Math.floor(Math.random() * arr.length);

alert( arr[rand] );