is it possible to preview local images before uploading them via a form?

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To be more specific, I want to use a form with one or more file input fields used for images. When those fields are changed, I\'d like to show a preview of the associated im

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一整个雨季

2020-12-02 21:36

The first step is finding out the image path. JavaScript is allowed to interrogate the upload control for a filename/path, but (for reasons of security) various browsers show different things to the JS engine than they display to the user - they tend to keep the filename intact so you can at least validate its extension, but you may get c:\fake_path\ or some similarly obfuscated thing prepended to the filename. Trying this on various browsers will give you an idea as to what gets returned as a real path, and what gets faked out, and where.

The second step is displaying the image. It's possible to display local images if you know their paths, via img tags with file:// source URLs, if the user's browser allows the file:// scheme. (Firefox doesn't, by default.) So if you can get the user to tell you what the full path to the image is, you can at least try to load it.

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暗喜

2020-12-02 21:36

Here's a jQuery + PHP script for uploading an image an previewing it.

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梦如初夏

2020-12-02 21:40

I have only ever seen Java applets that do this, for example, the image uploading applet on Facebook. The downside to the Java approach is that the user will be prompted to trust the applet before it runs, which is a kind of annoyance, but this allows the applet to present a file browser with image previews or do more interesting things like allows the user to upload an entire directory.

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暖寄归人

2020-12-02 21:42

No need for fancy stuff. All you need is the createObjectURL function, which creates a URL that can be used as the image src, and can come straight from a local file.

Let's say you selected a couple of images from the user's computer using a file input element (<input type="file" />). Here's how you would create previews for image files for it:

function createObjectURL(object) {
    return (window.URL) ? window.URL.createObjectURL(object) : window.webkitURL.createObjectURL(object);
}

function revokeObjectURL(url) {
    return (window.URL) ? window.URL.revokeObjectURL(url) : window.webkitURL.revokeObjectURL(url);
}

function myUploadOnChangeFunction() {
    if(this.files.length) {
        for(var i in this.files) {
            var src = createObjectURL(this.files[i]);
            var image = new Image();
            image.src = src;
            // Do whatever you want with your image, it's just like any other image
            // but it displays directly from the user machine, not the server!
        }
    }
}

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情深已故

2020-12-02 21:44

JavaScript has no access to the local file system for security purposes, period.

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庸人自扰

2020-12-02 21:44

You can try this approach, although it seems it doesn't work on IE.

http://saravani.wordpress.com/2012/03/14/preview-of-an-image-before-it-is-uploaded/

It's simple and fast to code.

I put the code here just in case the source dies:

Script:

    <!-- Assume jQuery is loaded -->
    <script>
      function readURL(input) {
        if (input.files && input.files[0]) {
          var reader = new FileReader();

          reader.onload = function (e) {
            $('#img_prev')
              .attr('src', e.target.result)
              .width(150)
              .height(200);
          };

          reader.readAsDataURL(input.files[0]);
        }
      }
    </script>

In the HTML:

    <!--[if IE]>
      <script src="http://html5shiv.googlecode.com/svn/trunk/html5.js"></script>
    <![endif]-->
    </head>
    <body>
      <input type='file' onchange="readURL(this);" />
      <img id="img_prev" src="#" alt="your image" />
    </body>

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