当分钟<时，你错过了连接字符串10 和秒< 10 所以你没有得到理想的结果。

You missed concatenating the string when minutes < 10 and seconds < 10 so you were not getting the desired result.

使用 Number（）$ c将字符串转换为数字$ c>并正确使用它，如下面的工作代码段所示：

Convert string to number using Number() and use it appropriately as shown in the working code snippet below:

编辑：更新后的代码 Number（）声明小时，分钟和秒。

Updated code to use Number() while declaration of hours, minutes and seconds.

var time = "16:30:00"; // your input

time = time.split(':'); // convert to array

// fetch
var hours = Number(time[0]);
var minutes = Number(time[1]);
var seconds = Number(time[2]);

// calculate
var timeValue;

if (hours > 0 && hours <= 12) {
  timeValue= "" + hours;
} else if (hours > 12) {
  timeValue= "" + (hours - 12);
} else if (hours == 0) {
  timeValue= "12";
}
 
timeValue += (minutes < 10) ? ":0" + minutes : ":" + minutes;  // get minutes
timeValue += (seconds < 10) ? ":0" + seconds : ":" + seconds;  // get seconds
timeValue += (hours >= 12) ? " P.M." : " A.M.";  // get AM/PM

// show
alert(timeValue);
console.log(timeValue);

阅读： Number（） | MDN

Read up: Number() | MDN