JSFiddle - React, Tailwind, and code Playground

JavaScript

Number.prototype.toMMSS = function () { 
    d = this;
    var sign = d < 0 ? "-" : "";
    var min = Math.floor(Math.abs(d))
    var sec = Math.floor((Math.abs(d) * 60) % 60);
    return sign + (min < 10 ? "0" : "") + min + ":" + (sec < 10 ? "0" : "") + sec;
};

console.log(12.5.toMMSS());       // "08:15"