需要为在线测验创建倒数计时器。 用户进入网页后，计时器应立即启动。
尝试了这段代码。
<
script >
var fiveMinutes = 3600;
var display = document.getElementById('time');
var myTimer;
function startTime(duration, display) {
var start = Date.now(),
diff,
minutes,
seconds;
function timer() {
diff = duration - (((Date.now() - start) / 1000) | 0);
minutes = (diff / 60) | 0;
seconds = (diff % 60) | 0;
minutes = minutes < 10 ? "0" + minutes : minutes;
seconds = seconds < 10 ? "0" + seconds : seconds;
display.textContent = minutes + ":" + seconds;
if (diff <= 0) {
display.textContent = "TIME IS UP!";
clearInterval(myTimer);
}
};
timer();
myTimer = setInterval(timer, 1000);
}
window.onload = function() {
startTime(fiveMinutes, display);
};
不是从当前时刻开始计数，而是从startTime变量中指定的日期开始计数。为了方便起见，我们考虑它与Date.now（）的返回值完全相同的格式。
我需要获取一个变量，为其提供一个值（不是Date.now（）），并将其用作起点
事先感谢
答案 0 :(得分：0)
所以我不确定这是否是您想要的。当用户进入页面时，这将触发。但是您的评论令人困惑。您是要在页面加载时还是在某个时间基于变量启动此操作？
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</html>答案 1 :(得分：0)
不确定这是否是您要查找的内容，但这是一个简单的倒计时计时器，可在窗口中显示时间。
const display = document.getElementById('time');
const fiveminutes = 5 * 60 * 1000;
function timer(endTime) {
var myTimer = setInterval(function() {
let now = new Date().getTime();
let diff = endTime - now;
let minutes = Math.floor(diff % (1000 * 60 * 60) / (1000 * 60));
let seconds = Math.floor(diff % (1000 * 60) / 1000);
minutes = minutes < 10 ? `0${minutes}` : minutes;
seconds = seconds < 10 ? `0${seconds}` : seconds;
display.textContent = minutes + ":" + seconds;
if (diff <= 0) {
display.textContent = "TIME IS UP!";
clearInterval(myTimer);
}
}, 100);
}
window.onload = timer(new Date().getTime() + fiveminutes);span {
font-family: calibri;
font-size: 4em;
}<body>
<span id="time"></span>
答案 2 :(得分：0)
这是我一直在努力的事情，我在这里尝试为您提供解决方案。它仍然是越野车，但是也许它会给您一些想法，并且我将在有更多时间时尝试对其进行编辑。 （我希望它现在可以正常工作，但需要一些休息。）
const
timeInput = document.getElementById("timeInput"),
nowBtn = document.getElementById("nowBtn"),
durationInput = document.getElementById("durationInput"),
confirmBtn = document.getElementById("confirmBtn"),
display = document.getElementById("display");
let
startTime,
timeRemaining,
chronos;
document.addEventListener("click", setUpTimer);
timeInput.addEventListener("focus", ()=>{ nowBtn.checked = false; });
function setUpTimer(event){
// Makes sure the button was the target of the click before proceeding
if(event.target == confirmBtn){
if(nowBtn.checked){ // Puts the current time in the time input
const
clickTime = new Date(),
hours = clickTime.getHours();
let minutes = clickTime.getMinutes();
clickTime.setSeconds(clickTime.getSeconds() + 1);
minutes = minutes < 10 ? "0" + minutes : minutes;
timeInput.value = `${hours}:${minutes}`;
}
const
timeInputValue = timeInput.value,
durationInputValue = durationInput.value;
// Validates input (or complains and aborts)
if(!timeInputValue || !durationInputValue){
display.innerHTML = "Please choose a start time and duration"
clearInterval(chronos);
return;
}
const
startArray = timeInputValue.split(":"),
startHours = parseInt(startArray[0]),
startMinutes = parseInt(startArray[1]),
durationInMinutes = parseInt(durationInput.value),
now = new Date();
// Updates global variables that `countdown` function will need
timeRemaining = durationInMinutes * 60;
startTime = new Date();
startTime.setHours(startHours, startMinutes);
// In case startTime is supposed to be tomorrow
const
nowHrs = now.getHours(),
strtHrs = startTime.getHours()
nowMins = now.getMinutes(),
strtMins = startTime.getMinutes();
// If it looks like the hour already passed, it's probably an earlier hour tomorrow
if(strtHrs < nowHrs || (strtHrs == nowHrs && strtMins < nowMins)){
startTime.setDate(startTime.getDate() + 1);
}
// Announces successful timer setup and resets inputs
const
displayedHours = startTime.getHours(),
storedMinutes = startTime.getMinutes(),
displayedMinutes = storedMinutes < 10 ? "0" + storedMinutes : storedMinutes;
display.innerHTML = `A ${durationInMinutes}-minute timer will start ` + `at ${displayedHours}:${displayedMinutes}`;
timeInput.value = "";
nowBtn.checked = false;
durationInput.value = "5";
// `setInterval` calls `countdown` function every second
console.log(startTime.toLocaleString());
clearInterval(chronos);
chronos = setInterval(countdown, 1000);
}
}
function countdown(){
if(timeRemaining <= 0){
display.innerHTML = "TIME IS UP!";
clearInterval(chronos);
}
else{
const now = new Date();
if(now.getTime() >= startTime.getTime()){
updateDisplayedTime(timeRemaining--);
}
}
}
function updateDisplayedTime(totalSeconds){
let
minutes = Math.floor(totalSeconds / 60),
seconds = totalSeconds % 60;
minutes = minutes < 10 ? "0" + minutes : minutes;
seconds = seconds < 10 ? "0" + seconds : seconds;
display.innerHTML = `${minutes}:${seconds}`;
}.inputContainer{ margin-bottom: 1em; }
#display{ font-size: 1.7em;}
#nowBtn {margin-left: 1em; }<div class="inputContainer">
<label>
<div>Start timer at: </div>
<input type="time" id="timeInput" />
</label>
<label>
<input type ="checkbox" id="nowBtn" />
<span>Now</span>
</label>
</div>
<div class="inputContainer">
<label>
<div>Duration (minutes): </div>
<input type="number" value="5" id="durationInput" min="1" max="1440" />
</label>
</div>
<div class="inputContainer">
<button id="confirmBtn">Confirm</button>
</div>
<div id="display"></div>