javascript - 简单的 JavaScript 计数器(不使用 jQuery 或其他框架)

Question

我需要一个简单的 JavaScript 计数器，它在页面加载时从 0 开始计数，一直计数到 HTML 中定义的数字。

这是 jQuery 版本...我怎样才能用纯 JavaScript 做同样的事情？

$('.count').each(function () {
    $(this).prop('Counter',0).animate({
        Counter: $(this).text()
    }, {
        duration: 4000,
        easing: 'swing',
        step: function (now) {
            $(this).text(Math.ceil(now));
        }
    });
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<span class="count">200</span>%

Answer 1

忽略缓动，您可以使用window.requestAnimationFrame创建一个简单的线性计数器。

let start // set on the first step to the timestamp provided
const el = document.getElementById('count') // get the element
const final = parseInt(el.textContent, 10) // parse out the final number
const duration = 4000 // duration in ms
const step = ts => {
  if (!start) {
    start = ts
  }
  // get the time passed as a fraction of total duration
  let progress = (ts - start) / duration 

  el.textContent = Math.floor(progress * final) // set the text
  if (progress < 1) {
    // if we're not 100% complete, request another animation frame
    requestAnimationFrame(step) 
  }
}

// start the animation
requestAnimationFrame(step)

<span id="count">200</span>%