JQuery/javascript : how to get file input value?

Question

我使用这个功能:

function resize(file, max_width, max_height, compression_ratio, imageEncoding){
    var fileLoader = new FileReader(),
    canvas = document.createElement('canvas'),
    context = null,
    imageObj = new Image(),
    blob = null;

    //create a hidden canvas object we can use to create the new resized image data
    canvas.id     = "hiddenCanvas";
    canvas.width  = max_width;
    canvas.height = max_height;
    canvas.style.visibility   = "hidden";
    document.body.appendChild(canvas);

    //get the context to use
    context = canvas.getContext('2d');

    // check for an image then
    //trigger the file loader to get the data from the image
    if (file.type.match('image.*')) {
        fileLoader.readAsDataURL(file);
    } else {
        alert('File is not an image' + file);
    }

    // setup the file loader onload function
    // once the file loader has the data it passes it to the
    // image object which, once the image has loaded,
    // triggers the images onload function
    fileLoader.onload = function() {
        var data = this.result;
        imageObj.src = data;
    };

    fileLoader.onabort = function() {
        alert("The upload was aborted.");
    };

    fileLoader.onerror = function() {
        alert("An error occured while reading the file.");
    };


    // set up the images onload function which clears the hidden canvas context,
    // draws the new image then gets the blob data from it
    imageObj.onload = function() {

        // Check for empty images
        if(this.width == 0 || this.height == 0){
            alert('Image is empty');
        } else {

            context.clearRect(0,0,max_width,max_height);
            context.drawImage(imageObj, 0, 0, this.width, this.height, 0, 0, max_width, max_height);


            //dataURItoBlob function available here:
            // http://stackoverflow.com/questions/12168909/blob-from-dataurl
            blob = dataURItoBlob(canvas.toDataURL(imageEncoding));

            //pass this blob to your upload function
            $( "#imgcaptmobile" ).append( '<img id="imagecaptmobile" src="' + blob + '" >');
        }
    };

    imageObj.onabort = function() {
        alert("Image load was aborted.");
    };

    imageObj.onerror = function() {
        alert("An error occured while loading image.");
    };

}

使用这个 html 代码:

<input type=\"text\" name=\"form_titre_photo_capture_mobile\" placeholder=\"Titre\" class=\"texte_texte_photo_capture_mobile\" id=\"form_titre_photo_capture_mobile\">
                            <input type=\"file\" capture=\"camera\" accept=\"image/*\" id=\"takePictureField\" name=\"takePictureField\">
                            <canvas id=\"canvas_captimg\" width=\"487\" height=\"365\"></canvas>
                            <div id=\"imgcaptmobile\" style=\"display:hidden\"></div>

我无法获取“file”变量来执行该函数!我已经尝试过:

$('#takePictureField').change(function(e) {
    var file = $(this).val();
    console.log($(this).val());
    resize(file, 487, 800, 70, "image/jpeg");
});

但是控制台日志上的错误是“Uncaught TypeError: Cannot call method 'match' of undefined”(当调用 if (file.type.match('image.*')) { 时)所以我想我没有正确调用文件输入值？...

Answer 1

那是因为 val 返回一个字符串对象，即所选文件的名称，而不是您的代码期望的 file 对象，您需要使用 files 属性:

$('#takePictureField').change(function(e) {
    var file = this.files; // this.files[0] => the first selected file object
    resize(file, 487, 800, 70, "image/jpeg");
});