Use Math.random() to generate a random 24-bit (6 * 4bits) hexadecimal number. Use bit shifting and then convert it to an hexadecimal string using Number.prototype.toString().
Also check out this random color generator.
const randomHexColorCode = () => {
let n = (Math.random() * 0xfffff * 1000000).toString(16);
return '#' + n.slice(0, 6);
};
// EXAMPLE
randomHexColorCode(); // '#e34155'
