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

我想知道图像何时完成加载.有没有办法通过回调来做到这一点?

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

如果没有，有没有办法做到这一点?

If not, is there a way to do it at all?

推荐答案

.complete + callback

.complete + callback

这是一种符合标准的方法，没有额外的依赖，等待时间不会超过必要的:

This is a standards compliant method without extra dependencies, and 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')
  })
}

来源:http://www.html5rocks.com/en/tutorials/es6/承诺/

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