方法1：

const paddingZeroLeft = (str, length) => {
    if(typeof (str) !== "string"){
        str = str + "";
    }
    if (str.length >= length){
        return str;
    } else {
        return paddingZeroLeft("0" + str, length);
    }
};
let second = 300;
let mm = paddingZeroLeft(parseInt(vm.refreshCount / 60), 2);
let ss = paddingZeroLeft(parseInt(vm.refreshCount % 60), 2);
let text = '';
text = `0${mm}:${ss}`;
// 05:00

方法2：

引入moment.js

let second = 300;
let text = moment.utc(moment.duration(second, "s").asMilliseconds()).format("HH:mm:ss") || "-";