如何创建JavaScript回调以了解何时加载图像？ [英] How to create a JavaScript callback for knowing when an image is loaded?

问题描述

我想知道图片何时加载完毕。有没有办法用回调来做？

I want to know when an image has finished loading. Is there a way to do it with a callback?

如果没有，有办法吗？

推荐答案

.complete + callback 符合标准，无库方式。这等待不超过必要时间：

.complete + callback is a standards compliant, no library way. This waits no longer than necessary:

var img = document.querySelector('img')

function loaded() {
  alert('loaded')
}

if (img.complete) {
  loaded()
} else {
  img.addEventListener('load', loaded)
  img.addEventListener('error', function() {
      alert('error')
  })
}

资料来源： http://www.html5rocks.com/en/tutorials/es6/promises/

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