在上传之前预览图像

这个解决方案怎么样？

只需将数据属性“data-type=editable”添加到图像标签，如下所示：

<img data-type="editable" id="companyLogo" src="http://www.coventrywebgraphicdesign.co.uk/wp-content/uploads/logo-here.jpg" height="300px" width="300px" />

而且你的项目的脚本当然......

function init() {
    $("img[data-type=editable]").each(function (i, e) {
        var _inputFile = $('<input/>')
            .attr('type', 'file')
            .attr('hidden', 'hidden')
            .attr('onchange', 'readImage()')
            .attr('data-image-placeholder', e.id);

        $(e.parentElement).append(_inputFile);

        $(e).on("click", _inputFile, triggerClick);
    });
}

function triggerClick(e) {
    e.data.click();
}

Element.prototype.readImage = function () {
    var _inputFile = this;
    if (_inputFile && _inputFile.files && _inputFile.files[0]) {
        var _fileReader = new FileReader();
        _fileReader.onload = function (e) {
            var _imagePlaceholder = _inputFile.attributes.getNamedItem("data-image-placeholder").value;
            var _img = $("#" + _imagePlaceholder);
            _img.attr("src", e.target.result);
        };
        _fileReader.readAsDataURL(_inputFile.files[0]);
    }
};

// 
// IIFE - Immediately Invoked Function Expression
// https://stackoverflow.com/questions/18307078/jquery-best-practises-in-case-of-document-ready
(

function (yourcode) {
    "use strict";
    // The global jQuery object is passed as a parameter
    yourcode(window.jQuery, window, document);
}(

function ($, window, document) {
    "use strict";
    // The $ is now locally scoped 
    $(function () {
        // The DOM is ready!
        init();
    });

    // The rest of your code goes here!
}));

See demo at JSFiddle

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在使用 jQuery/javascript 上传之前预览多个图像？

这将一次将多个文件预览为缩略图

html

<input id="ImageMedias" multiple="multiple" name="ImageMedias" type="file"
accept=".jfif,.jpg,.jpeg,.png,.gif" class="custom-file-input"  value="">                                    
<div id="divImageMediaPreview"></div>

脚本

$("#ImageMedias").change(function () {
    if (typeof (FileReader) != "undefined") {
        var dvPreview = $("#divImageMediaPreview");
        dvPreview.html("");            
        $($(this)[0].files).each(function () {
            var file = $(this);                
                var reader = new FileReader();
                reader.onload = function (e) {
                    var img = $("<img />");
                    img.attr("style", "width: 150px; height:100px; padding: 10px");
                    img.attr("src", e.target.result);
                    dvPreview.append(img);
                }
                reader.readAsDataURL(file[0]);                
        });
    } else {
        alert("This browser does not support HTML5 FileReader.");
    }
});

Working Demo on Codepen

Working Demo on jsfiddle

我希望这将有所帮助。

---

感谢互联网，我做了一个可以在IE 7+中生成预览效果的插件，但限制很少。我将它放入 github page 以便更容易获得它

$(function () { $("input[name=file1]").previewimage({ div: ".preview", imgwidth: 180, imgheight: 120 }); $("input[name=file2]"). previewimage({ div: ".preview2", imgwidth: 90, imgheight: 90 }); }); .preview > div { display: inline-block;文本对齐：居中； } .preview2 > div { 显示：内联块；文本对齐：居中； } 预览

Preview2

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对于多张图片上传（修改@IvanBaev 的解决方案）

function readURL(input) {
    if (input.files && input.files[0]) {
        var i;
        for (i = 0; i < input.files.length; ++i) {
          var reader = new FileReader();
          reader.onload = function (e) {
              $('#form1').append('<img src="'+e.target.result+'">');
          }
          reader.readAsDataURL(input.files[i]);
        }
    }
}

http://jsfiddle.net/LvsYc/12330/

希望这可以帮助某人。

---

这是我的代码。支持IE[6-9]、chrome 17+、firefox、Opera 11+、Maxthon3

函数 previewImage(fileObj, imgPreviewId) { var allowExtention = ".jpg,.bmp,.gif,.png"; //允许上传文件类型 document.getElementById("hfAllowPicSuffix").value; var 扩展 = fileObj.value.substring(fileObj.value.lastIndexOf(".") + 1).toLowerCase(); var browserVersion = window.navigator.userAgent.toUpperCase(); if (allowExtention.indexOf(extention) > -1) { if (fileObj.files) { if (window.FileReader) { var reader = new FileReader(); reader.onload = function (e) { document.getElementById(imgPreviewId).setAttribute("src", e.target.result); }; reader.readAsDataURL(fileObj.files[0]); } else if (browserVersion.indexOf("SAFARI") > -1) { alert("不支持 Safari6.0 以下浏览器"); } } else if (browserVersion.indexOf("MSIE") > -1) { if (browserVersion.indexOf("MSIE 6") > -1) {//ie6 document.getElementById(imgPreviewId).setAttribute("src",文件对象值）； } else {//ie[7-9] fileObj.select(); fileObj.blur(); var newPreview = document.getElementById(imgPreviewId); newPreview.style.border = "实心 1px #eeeeee"; newPreview.style.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod='scale',src='" + document.selection.createRange().text + "')"; newPreview.style.display = "块"; } } else if (browserVersion.indexOf("FIREFOX") > -1) {//firefox var firefoxVersion = parseFloat(browserVersion.toLowerCase().match(/firefox\/([\d.]+)/)[1 ]); if (firefoxVersion < 7) {//firefox7 下面 document.getElementById(imgPreviewId).setAttribute("src", fileObj.files[0].getAsDataURL()); } else {//firefox7.0+ document.getElementById(imgPreviewId).setAttribute("src", window.URL.createObjectURL(fileObj.files[0])); } } else { document.getElementById(imgPreviewId).setAttribute("src", fileObj.value); } } else { alert("仅支持" + allowExtention + "suffix"); fileObj.value = ""; //清除选择的文件 if (browserVersion.indexOf("MSIE") > -1) { fileObj.select(); document.selection.clear(); } } } function changeFile(elem) { //file object , preview img tag id previewImage(elem,'imagePreview') } < img src="" id="imagePreview" style="width:120px;height:80px;" alt=""/>

---

默认图片

                @Html.TextBoxFor(x => x.productModels.DefaultImage, new {@type = "file", @class = "form-control", onchange = "openFile(event)", @name = "DefaultImage", @id = "DefaultImage" })
                @Html.ValidationMessageFor(model => model.productModels.DefaultImage, "", new { @class = "text-danger" })
                    <img src="~/img/ApHandler.png"  style="height:125px; width:125px" id="DefaultImagePreview"/>
            </div>

 <script>
    var openFile = function (event) {
        var input = event.target;

        var reader = new FileReader();
        reader.onload = function () {
            var dataURL = reader.result;
            var output = document.getElementById('DefaultImagePreview');
            output.src = dataURL;
        };
        reader.readAsDataURL(input.files[0]);
    };
</script>

---

如果你使用 React，这里有一个解决方案：

import * as React from 'react'
import { useDropzone } from 'react-dropzone'

function imageDropper() {
  const [imageUrl, setImageUrl] = React.useState()
  const [imageFile, setImageFile] = React.useState()

  const onDrop = React.useCallback(
    acceptedFiles => {
      const file = acceptedFiles[0]
      setImageFile(file)

      // convert file to data: url
      const reader = new FileReader()
      reader.addEventListener('load', () => setImageUrl(String(reader.result)), false)
      reader.readAsDataURL(file)
    },
    [setImageFile, setImageUrl]
  )
  const { getRootProps, getInputProps, isDragActive } = useDropzone({ onDrop })

  return (
    <div>
      <div {...getRootProps()}>
        {imageFile ? imageFile.name : ''}
        {isDragActive ? <p>Drop files here...</p> : <p>Select image file...</p>}
        <input {...getInputProps()} />
      </div>
      {imageUrl && (
        <div>
          Your image: <img src={imageUrl} />
        </div>
      )}
    </div>
  )
}

---

<img id="blah" alt="your image" width="100" height="100" />
<input type="file" name="photo" id="fileinput" />
<script>
$('#fileinput').change(function() {
var url = window.URL.createObjectURL(this.files[0]);
 $('#blah').attr('src',url);
});
</script>

---

https://stackoverflow.com/a/59985954/8784402

ES2017 方式

// 将文件转换为 base64 url const readURL = file => { return new Promise((res, rej) => { const reader = new FileReader(); reader.onload = e => res(e.target.result) ; reader.onerror = e => rej(e); reader.readAsDataURL(file); }); }; // 用于演示 const fileInput = document.createElement('input'); fileInput.type = '文件'; const img = document.createElement('img'); img.attributeStyleMap.set('max-width', '320px'); document.body.appendChild(fileInput); document.body.appendChild(img); const preview = async event => { const file = event.target.files[0]; const url = 等待 readURL(file); img.src = 网址； }; fileInput.addEventListener('change', preview);

---

这是使用纯 javascript 在上传之前预览图像的一种非常简单的方法；

//profile_change is the id of the input field where we choose an image
document.getElementById("profile_change").addEventListener("change", function() {

//Here we select the first file among the selected files.
const file = this.files[0];

/*here i used a label for the input field which is an image and this image will 
  represent the photo selected and profile_label is the id of this label */
const profile_label = document.getElementById("profile_label");

//Here we check if a file is selected
if(file) {
    //Here we bring in the FileReader which reads the file info. 
    const reader = new FileReader();
    
    /*After reader loads we change the src attribute of the label to the url of the 
    new image selected*/
    reader.addEventListener("load", function() {
        dp_label.setAttribute("src", this.result);
    })

    /*Here we are reading the file as a url i.e, we try to get the location of the 
    file to set that as the src of the label which we did above*/
    reader.readAsDataURL(file);

}else {
    //Here we simply set the src as default, whatever you want if no file is selected.
    dp_label.setAttribute("src", "as_you_want")
}
});

这是HTML；

<label for="profile_change">
            <img title="Change Profile Photo" id="profile_label" 
             src="as_you_want" alt="DP" style="height: 150px; width: 150px; 
               border-radius: 50%;" >
</label>
<input style="display: none;" id="profile_change" name="DP" type="file" class="detail form-control">

---

对于我的应用程序，使用加密的 GET url 参数，只有这个有效。我总是得到一个TypeError: $(...) is null。取自 https://developer.mozilla.org/en-US/docs/Web/API/FileReader/readAsDataURL

函数 previewFile() { var preview = document.querySelector('img'); var file = document.querySelector('input[type=file]').files[0]; var reader = new FileReader(); reader.addEventListener("load", function () { preview.src = reader.result; }, false); if (file) { reader.readAsDataURL(file); } }

---

function assignFilePreviews() {
    $('input[data-previewable=\"true\"]').change(function() {
        var prvCnt = $(this).attr('data-preview-container');
        if (prvCnt) {
            if (this.files && this.files[0]) {
                var reader = new FileReader();
                reader.onload = function(e) {
                    var img = $('<img>');
                    img.attr('src', e.target.result);
                    img.error(function() {
                        $(prvCnt).html('');
                    });
                    $(prvCnt).html('');
                    img.appendTo(prvCnt);
                }
                reader.readAsDataURL(this.files[0]);
            }
        }
    });
}
$(document).ready(function() {
    assignFilePreviews();
});

HTML

<input type="file" data-previewable="true" data-preview-container=".prd-img-prv" />
<div class = "prd-img-prv"></div>

This also handles case when file with invalid type ( ex. pdf ) is choosen

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