How to show image preview before Upload?

问题

I want to show image preview before uploading process. In my case I selected multiple images with input file and the list of file name will show as link. When I click on the image file name link then the preview image popup will show of it's specific image. Here is my code..

<input id="uploadBtn" type="file" class="upload" multiple="multiple" name="browsefile" style="display: none !important;"/>

<input type="button" value="ファイル追加" onclick="document.getElementById('uploadBtn').click();" style="float: right;"/>

<input id="filename" type="hidden" />
<br>
<div id="upload_prev"></div>
<div style="clear:both;"></div>

Here is my javascript

<script type="text/javascript">
  $(document).on('click','.close',function(){
    $(this).parents('span').remove();
  })

  document.getElementById("uploadBtn").onchange = function () {
     document.getElementById("uploadFile").value = this.value;
  };

  document.getElementById('uploadBtn').onchange = uploadOnChange;

  function uploadOnChange() {
    var filename = this.value;
    var lastIndex = filename.lastIndexOf("\\");
    if (lastIndex >= 0) {
    filename = filename.substring(lastIndex + 1);
  }
var files = $('#uploadBtn')[0].files;
for (var i = 0; i < files.length; i++) {
  $("#upload_prev").append('<span><br><div class="col-md-10"><span class="uploadFiles">'+ '<a href="">' +files[i].name+ '</a>' +'</span></div><div class="col-md-2"><p class="close" style="font-size: 13pt;">削除</p><br></div></span>');
}
document.getElementById('filename').value = filename;
}
</script>

Here is Screenshot

回答1:

You can use URL.createObjectURL() to create a Blob URL of uploaded image.

Adjusted html to <div> as appended parent element instead of <span> element.

At first click at <a> element, if next <div> does not contain <img> append <img> else call .toggle() to display <img>.

At click at .close element, call .toggle() instead of .remove().

You can also include an element, for example, <button>, which when clicked, creates a FormData instance to set all or selected File objects as entries of multipart/form-data to upload to server.

$(document).on('click', '.close', function() {
  $(this).siblings("img").toggle();
})

document.getElementById("uploadBtn").onchange = function() {
  document.getElementById("uploadFile").value = this.value;
};

document.getElementById('uploadBtn').onchange = uploadOnChange;

function uploadOnChange() {
  var filename = this.value;
  var lastIndex = filename.lastIndexOf("\\");
  if (lastIndex >= 0) {
    filename = filename.substring(lastIndex + 1);
  }
  var files = $('#uploadBtn')[0].files;
  for (var i = 0; i < files.length; i++) {
    (function(i) {
      $("#upload_prev").append('<div><br><div class="col-md-10"><span class="uploadFiles">' + '<a href="">' + files[i].name + '</a>' + '</span></div><div class="col-md-2"><p class="close" style="font-size: 13pt;">削除</p><br></div></div>');
      $("#upload_prev a:contains(" + files[i].name + ")")
        .on("click", function(e) {
          e.preventDefault();
          var close = $(this).closest("div")
            .next("div")
            .find(".close");
          if (!$(this).closest("div")
            .next("div").find("img").length) 
            close
            .after(
              $("<img>", {
                src: URL.createObjectURL(files[i])
              })
            )
          else
            close.siblings("img").toggle()
        })
    })(i);
  }

  document.getElementById('filename').value = filename;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input id="uploadBtn" type="file" class="upload" multiple="multiple" accept="image/*" name="browsefile" style="display: none !important;" />

<input type="button" value="ファイル追加" onclick="document.getElementById('uploadBtn').click();" style="float: right;" />

<input id="filename" type="hidden" />
<br>
<div id="upload_prev"></div>
<div style="clear:both;"></div>

回答2:

use FileReader, see How to show local picture in web page?

if no support, you can upload to server tmp dir first, then preview

$('#tmp_img').attr('src','tmp/tmp_hashnumber.jpg');

move it after make sure

回答3:

I think you are looking something like this. This is part of my previous solution. Here you will find a more complex implementation

//Console logging (html)
if (!window.console)
  console = {};

var console_out = document.getElementById('console_out');

console.log = function(message) {
  console_out.innerHTML += message + '<br />';
  console_out.scrollTop = console_out.scrollHeight;
}

function previewFile() { 
  var preview = document.getElementById('source_image');
  var file   = document.querySelector('input[type=file]').files[0]; 
  var reader  = new FileReader();
  reader.addEventListener("load", function(e) {
    preview.src = e.target.result; 
    preview.onload = function() {
      console.log('Image Loaded');
    };
  }, false);

  if (file) {  
    reader.readAsDataURL(file);
  }
}

<input type="file" onchange="previewFile()"><br>
<div>
  <h3>Original Image before Upload</h3>
  <img id="source_image" alt="Image preview..." />
</div>

<div>
  <fieldset>
    <legend>Console output</legend>
    <div id='console_out'></div>
  </fieldset>
</div>

来源：https://stackoverflow.com/questions/43729171/how-to-show-image-preview-before-upload