javaScript是一种无类型语言，这意味着它在某些情况下非常灵活，但在另一方面，您可能会发现自己会遇到意想不到结果，特别是当您没有实现适当的控件时。
在您代码中，您试图通过连接数字和字符串来返回一些数学运算：

total = hoursDifference + ":" + minutesDifference + ":" +secondsDifference;

但是你应该使用反勾号来达到预期的效果：

`${hoursDifference}:${minutesDifference}:${secondsDifference}`

function timeDifference(laterdate, earlierdate) {
    var difference = laterdate.getTime() - earlierdate.getTime();
    var daysDifference = Math.floor(difference / 1000 / 60 / 60 / 24);
    difference -= daysDifference * 1000 * 60 * 60 * 24
    var hoursDifference = Math.floor(difference / 1000 / 60 / 60);
    difference -= hoursDifference * 1000 * 60 * 60
    var minutesDifference = Math.floor(difference / 1000 / 60);
    difference -= minutesDifference * 1000 * 60
    var secondsDifference = Math.floor(difference / 1000);
    total =  `${hoursDifference}:${minutesDifference}:${secondsDifference}`;
    return total;
}

let laterdate = new Date("2022-12-13 10:00:48")
let earlierdate = new Date("2022-12-13 10:00:47")
console.log(timeDifference(laterdate,earlierdate))

型