在使用 Javascript 上传之前检查图像的宽度和高度

Question

我有一个 JPS，用户可以在其中放置图像：

<div class="photo">
    <div>Photo (max 240x240 and 100 kb):</div>
    <input type="file" name="photo" id="photoInput" onchange="checkPhoto(this)"/>
</div>

我已经写了这个js：

function checkPhoto(target) {
    if(target.files[0].type.indexOf("image") == -1) {
        document.getElementById("photoLabel").innerHTML = "File not supported";
        return false;
    }
    if(target.files[0].size > 102400) {
        document.getElementById("photoLabel").innerHTML = "Image too big (max 100kb)";
        return false;
    }
    document.getElementById("photoLabel").innerHTML = "";
    return true;
}

它可以很好地检查文件类型和大小。现在我想检查图像的宽度和高度，但我做不到。
我试过target.files[0].width，但我得到undefined。通过其他方式我得到0。
有什么建议吗？

Answer 1

function validateimg(ctrl) {
    var fileUpload = $("#txtPostImg")[0];
    var regex = new RegExp("([a-zA-Z0-9\s_\\.\-:])+(.jpg|.png|.gif)$");
    if (regex.test(fileUpload.value.toLowerCase())) {
        if (typeof (fileUpload.files) != "undefined") {
            var reader = new FileReader();
            reader.readAsDataURL(fileUpload.files[0]);
            reader.onload = function (e) {
                var image = new Image();
                image.src = e.target.result;
                image.onload = function () {
                    var height = this.height;
                    var width = this.width;
                    console.log(this);
                    if ((height >= 1024 || height <= 1100) && (width >= 750 || width <= 800)) {
                        alert("Height and Width must not exceed 1100*800.");
                        return false;
                    }
                    alert("Uploaded image has valid Height and Width.");
                    return true;
                };
            }
        } else {
            alert("This browser does not support HTML5.");
            return false;
        }
    } else {
        alert("Please select a valid Image file.");
        return false;
    }
}

Answer 2

我同意。一旦它被上传到用户浏览器可以访问的地方，那么很容易获得大小。由于您需要等待图像加载，您需要为img 挂钩到onload 事件。

更新示例：

// async/promise function for retrieving image dimensions for a URL
function imageSize(url) {
    const img = document.createElement("img");

    const promise = new Promise((resolve, reject) => {
      img.onload = () => {
        // Natural size is the actual image size regardless of rendering.
        // The 'normal' `width`/`height` are for the **rendered** size.
        const width  = img.naturalWidth;
        const height = img.naturalHeight; 

        // Resolve promise with the width and height
        resolve({width, height});
      };

      // Reject promise on error
      img.onerror = reject;
    });

    // Setting the source makes it start downloading and eventually call `onload`
    img.src = url;

    return promise;
}

// How to use in an async function
(async() => {
  const imageUrl = 'http://your.website.com/userUploadedImage.jpg';
  const imageDimensions = await imageSize(imageUrl);

  console.info(imageDimensions); // {width: 1337, height: 42}
})();

旧示例：

var width, height;

var img = document.createElement("img");
img.onload = function() {
    // `naturalWidth`/`naturalHeight` aren't supported on <IE9. Fallback to normal width/height
    // The natural size is the actual image size regardless of rendering.
    // The 'normal' width/height are for the **rendered** size.
    
    width  = img.naturalWidth  || img.width;
    height = img.naturalHeight || img.height; 
    
    // Do something with the width and height
}

// Setting the source makes it start downloading and eventually call `onload`
img.src = "http://your.website.com/userUploadedImage.jpg";

Answer 3

就我而言，我还需要阻止提交表单，所以这是对我有用的解决方案。

preventDefault 将停止表单动作，然后我们在 onload 函数中检查图像的大小和尺寸。

如果一切顺利，我们允许提交。

如果用户仍然尝试使用无效图像提交表单，则提交按钮会被禁用，因此我还必须在输入有效图像后重新启用提交按钮。

const validateMaxImageFileSize = (e) => {
  e.preventDefault();
  const el = $("input[type='file']")[0];

  if (el.files && el.files[0]) {
    const file = el.files[0];

    const maxFileSize = 5242880; // 5 MB
    const maxWidth = 1920;
    const maxHeight = 1080;

    const img = new Image();
    img.src = window.URL.createObjectURL(file);
    img.onload = () => {
      if (file.type.match('image.*') && file.size > maxFileSize) {
        alert('The selected image file is too big. Please choose one that is smaller than 5 MB.');
      } else if (file.type.match('image.*') && (img.width > maxWidth || img.height > maxHeight)) {
        alert(`The selected image is too big. Please choose one with maximum dimensions of ${maxWidth}x${maxHeight}.`);
      } else {
        e.target.nodeName === 'INPUT'
          ? (e.target.form.querySelector("input[type='submit']").disabled = false)
          : e.target.submit();
      }
    };
  }
};

$('form.validate-image-size').on('submit', validateMaxImageFileSize);
$("form.validate-image-size input[type='file']").on('change', validateMaxImageFileSize);

Answer 4

在我看来，您必须要求的完美答案是

var reader = new FileReader();

//Read the contents of Image File.
reader.readAsDataURL(fileUpload.files[0]);
reader.onload = function (e) {

  //Initiate the JavaScript Image object.
  var image = new Image();

  //Set the Base64 string return from FileReader as source.
  image.src = e.target.result;

  //Validate the File Height and Width.
  image.onload = function () {
    var height = this.height;
    var width = this.width;
    if (height > 100 || width > 100) {
      alert("Height and Width must not exceed 100px.");
      return false;
    }
    alert("Uploaded image has valid Height and Width.");
    return true;
  };
};

Answer 5

您可以在不显示图像的情况下执行预览步骤，所有浏览器都支持。以下 js 代码向您展示了如何检查 width 和 height ：

var file = e.target.files[0];
if (/\.(jpe?g|png|gif)$/i.test(file.name)) {
    var reader = new FileReader();
    reader.addEventListener("load", function () {
        var image = new Image();
        image.src = this.result as string;
        image.addEventListener('load', function () {
            console.log(`height: ${this.height}, width: ${this.width}`);
        });
                
    }, false);
            
    reader.readAsDataURL(file);
}

基于Mozilla docs:

readAsDataURL方法用于读取指定的内容 Blob 或 File。当读取操作完成时，readyState 变为DONE，触发loadend。当时result 属性包含作为数据的数据：表示文件的 URL 数据作为 base64 编码的字符串。

browser compatibility 也在列表中。

Answer 6

文件只是一个文件，你需要像这样创建一个图像：

var _URL = window.URL || window.webkitURL;
$("#file").change(function (e) {
    var file, img;
    if ((file = this.files[0])) {
        img = new Image();
        var objectUrl = _URL.createObjectURL(file);
        img.onload = function () {
            alert(this.width + " " + this.height);
            _URL.revokeObjectURL(objectUrl);
        };
        img.src = objectUrl;
    }
});

演示：http://jsfiddle.net/4N6D9/1/

我认为您意识到这仅在少数浏览器中受支持。主要是 firefox 和 chrome，现在也可能是 opera。

P.S. URL.createObjectURL() 方法已从 MediaStream 接口 中删除。此方法已在 2013 年弃用，并通过将流分配给 HTMLMediaElement.srcObject 来取代。旧方法已被删除，因为它不太安全，需要调用 URL.revokeOjbectURL() 来结束流。其他用户代理已弃用 (Firefox) 或删除 (Safari) 此功能。

更多信息请参考here。

Answer 7

    const ValidateImg = (file) =>{
        let img = new Image()
        img.src = window.URL.createObjectURL(file)
        img.onload = () => {
            if(img.width === 100 && img.height ===100){
                alert("Correct size");
                return true;
            }
            alert("Incorrect size");
            return true;
        }
    }

Answer 8

这是检查大小的最简单方法

let img = new Image()
img.src = window.URL.createObjectURL(event.target.files[0])
img.onload = () => {
   alert(img.width + " " + img.height);
}

检查具体尺寸。以 100 x 100 为例

let img = new Image()
img.src = window.URL.createObjectURL(event.target.files[0])
img.onload = () => {
   if(img.width === 100 && img.height === 100){
        alert(`Nice, image is the right size. It can be uploaded`)
        // upload logic here
        } else {
        alert(`Sorry, this image doesn't look like the size we wanted. It's 
   ${img.width} x ${img.height} but we require 100 x 100 size image.`);
   }                
}

Answer 9

将函数附加到输入类型文件的onchange方法/onchange="validateimg(this)"/

   function validateimg(ctrl) { 
        var fileUpload = ctrl;
        var regex = new RegExp("([a-zA-Z0-9\s_\\.\-:])+(.jpg|.png|.gif)$");
        if (regex.test(fileUpload.value.toLowerCase())) {
            if (typeof (fileUpload.files) != "undefined") {
                var reader = new FileReader();
                reader.readAsDataURL(fileUpload.files[0]);
                reader.onload = function (e) {
                    var image = new Image();
                    image.src = e.target.result;
                    image.onload = function () {
                        var height = this.height;
                        var width = this.width;
                        if (height < 1100 || width < 750) {
                            alert("At least you can upload a 1100*750 photo size.");
                            return false;
                        }else{
                            alert("Uploaded image has valid Height and Width.");
                            return true;
                        }
                    };
                }
            } else {
                alert("This browser does not support HTML5.");
                return false;
            }
        } else {
            alert("Please select a valid Image file.");
            return false;
        }
    }

Answer 10

function uploadfile(ctrl) {
    var validate = validateimg(ctrl);

    if (validate) {
        if (window.FormData !== undefined) {
            ShowLoading();
            var fileUpload = $(ctrl).get(0);
            var files = fileUpload.files;


            var fileData = new FormData();


            for (var i = 0; i < files.length; i++) {
                fileData.append(files[i].name, files[i]);
            }


            fileData.append('username', 'Wishes');

            $.ajax({
                url: 'UploadWishesFiles',
                type: "POST",
                contentType: false,
                processData: false,
                data: fileData,
                success: function(result) {
                    var id = $(ctrl).attr('id');
                    $('#' + id.replace('txt', 'hdn')).val(result);

                    $('#imgPictureEn').attr('src', '../Data/Wishes/' + result).show();

                    HideLoading();
                },
                error: function(err) {
                    alert(err.statusText);
                    HideLoading();
                }
            });
        } else {
            alert("FormData is not supported.");
        }

    }