randomIndex.js

// define a Array 
let array = ["String 1", "STRING 2", "String 3"];

// defining a new function named getRandomIndex
let getRandomIndex = array => {
    // get a random number between 0 and 1 and * by the array lenght
    let rand = Math.floor(Math.random() * array.length);
    
    // let the index is the random number from above
    let randIndex = array[rand];
    
    // return the array item
    return randIndex;
}