JavaScript |定时器

先决条件：

• 获取分钟（）
• GetSeconds()
• SetInterval() 方法

在这篇文章中，显示了一个计时器，它显示倒计时，并且它的颜色/消息在每个特定时间段后都会发生变化。

句法：

setTimeout(function, milliseconds, parameter1, ...)

参数：它接受下面指定的一些参数-

• 函数：它将被执行的函数。
• 毫秒：在执行代码之前等待的毫秒数。它是可选的，其默认值为零 (0)。
• parameter1：传递给函数的附加参数，可选。

返回值：返回一个数字，表示设置的定时器的ID值。

JavaScript 代码将计时器设置为 2 分钟，当时间到时页面警报“时间到”。 setTimeout() 方法在指定的毫秒数后调用函数或计算表达式。

实现计时器的 JavaScript 代码：

  

    
        //set minutes
        var mins = 2;
  
        //calculate the seconds
        var secs = mins * 60;
  
        //countdown function is evoked when page is loaded
        function countdown() {
            setTimeout('Decrement()', 60);
        }
  
        //Decrement function decrement the value.
        function Decrement() {
            if (document.getElementById) {
                minutes = document.getElementById("minutes");
                seconds = document.getElementById("seconds");
  
                //if less than a minute remaining
                //Display only seconds value.
                if (seconds < 59) {
                    seconds.value = secs;
                }
  
                //Display both minutes and seconds
                //getminutes and getseconds is used to
                //get minutes and seconds
                else {
                    minutes.value = getminutes();
                    seconds.value = getseconds();
                }
                //when less than a minute remaining
                //colour of the minutes and seconds
                //changes to red
                if (mins < 1) {
                    minutes.style.color = "red";
                    seconds.style.color = "red";
                }
                //if seconds becomes zero,
                //then page alert time up
                if (mins < 0) {
                    alert('time up');
                    minutes.value = 0;
                    seconds.value = 0;
                }
                //if seconds > 0 then seconds is decremented
                else {
                    secs--;
                    setTimeout('Decrement()', 1000);
                }
            }
        }
  
        function getminutes() {
            //minutes is seconds divided by 60, rounded down
            mins = Math.floor(secs / 60);
            return mins;
        }
  
        function getseconds() {
            //take minutes remaining (as seconds) away 
            //from total seconds remaining
            return secs - Math.round(mins * 60);
        }
    



  

    
        Time Left ::
         :
                        
        
    

  

输出：
点击运行按钮后——

一段时间后-

当还剩不到 1 分钟时——

当计时器到时-