JS+HTML实现自定义上传图片按钮并显示图片功能的方法分析

<!DOCTYPE html>
<html>
<head>
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
  <title>图片上传</title>
</head>
<body>
  <!-- 要将父布局的position设置为relative，父布局将无法包裹input -->
  <div style="position: relative;">
    <!--设置input的position为absolute，使其不按文档流排版，并设置其包裹整个布局 -->
    <!-- 设置opactity为0，使input变透明 -->
    <!-- 只接受jpg，gif和png格式 -->
    <input id="upload-input" style="position: absolute; top: 0; bottom: 0; left: 0;right: 0; opacity: 0;" type="file" accept="image/gif, image/jpg, image/png" />
    <!-- 自定义按钮效果 -->
    <div style="text-align: top">
      <span style="font-size: 12px;">上传文件：</span>
      <img id="upload" src="./upload.png" style="width: 40px; height: 40px; vertical-align: middle;" />
    </div>
  </div>
</body>
</html>

FileReader转Base64显示

<script type="text/javascript">
  function showImg(input) {
    var file = input.files[0];
    var reader = new FileReader()
    // 图片读取成功回调函数
    reader.onload = function(e) {
      document.getElementById('upload').src=e.target.result
    }
    reader.readAsDataURL(file)
  }
</script>

URL.createObjectURL创建临时URL

  function showImg(input) {
    var file = input.files[0];
    var url = window.URL.createObjectURL(file)
    document.getElemtById('upload').src=url
  }

单图上传代码示例

<input id="upload-input" style="position: absolute; top: 0; bottom: 0; left: 0;right: 0; opacity: 0;" 
type="file" accept="image/gif, image/jpg, image/png" 
onchange="showImg(this)"/>

多图上传实现

<input id="upload-input" 
style="position: absolute; top: 0; bottom: 0; left: 0;right: 0; opacity: 0;" type="file" 
accept="image/gif, image/jpg, image/png" multiple onchange="showImg(this)"/>

多图上传代码示例

<!DOCTYPE html>
<html>
<head>
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
  <title>图片上传</title>
</head>
<body>
  <!-- 要将父布局的position设置为relative，父布局将无法包裹input -->
  <div style="position: relative;">
    <!--设置input的position为absolute，使其不按文档流排版，并设置其包裹整个布局 -->
    <!-- 设置opactity为0，使input变透明 -->
    <!-- 只接受jpg，gif和png格式 -->
    <input id="upload-input" style="position: absolute; top: 0; bottom: 0; left: 0;right: 0; opacity: 0;" type="file" accept="image/gif, image/jpg, image/png" onchange="showImg(this)" multiple />
    <!-- 自定义按钮效果 -->
    <div style="text-align: top">
      <span style="font-size: 12px;">上传文件：</span>
      <img id="upload" src="./upload.png" style="width: 40px; height: 40px; vertical-align: middle;" />
    </div>
  </div>
  <div id="imgContainer" style="margin-top: 10px;"></div>
</body>
<script type="text/javascript">
  function showImg(obj) {
    var files = obj.files
    // document.getElementById("imgContainer").innerHTML = getImgsByUrl(files)
    getImgsByFileReader(document.getElementById("imgContainer"), files)
  }
  // 使用window.URL.createObjectURL(file)读取file实例并显示图片
  function getImgsByUrl(files) {
    var elements = ''
    for (var i = 0; i < files.length; i++) {
      var url = window.URL.createObjectURL(files[i])
      elements += "<img src='"+ url + "' style='width: 40px; height: 40px; vertical-align: middle; margin-right: 5px;' />"
    }
    return elements
  }
  // 使用FileReader读取file实例并显示图片
  function getImgsByFileReader(el, files) {
    for (var i = 0; i < files.length; i++) {
      let img = document.createElement('img')
      img.setAttribute('style', 'width: 40px; height: 40px; vertical-align: middle; margin-right: 5px;')
      el.appendChild(img)
      var reader = new FileReader()
      reader.onload = function(e) {
        img.src = e.target.result
      }
      reader.readAsDataURL(files[i])
    }
  }
</script>
</html>