Change color randomly in javascript

script.js

//live example at: https://playcode.io/448394

var makeColors = () => {
    var minNum = 0;
    var maxNum = 9;
    var minLet = 65;
    var maxLet = 71;

    function randomNumber() {
        return (Math.floor(Math.random() * (+maxNum - +minNum)) + +minNum).toString();
    };

    function randomLetter() {
        return String.fromCharCode((Math.floor(Math.random() * (+maxLet - +minLet)) + +minLet));
    };

    var color = [];
    color[0] = '#';

    for (let i = 1; i < 8; i++) {
        color[i] = randomNumber();
        color[i + 1] = randomLetter();
    }

    return color.join('');
}

var miliseconds = 200;
window.setInterval(function () {
    document.body.style = 'background-color: ' + makeColors() + '';
}, miliseconds);