如何使用FormData上传压缩裁剪后的图片Blob对象

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>使用FormData上传压缩裁剪后的图片Blob对象</title>
</head>

<body>
    <input type="file" name="myfile" id="myfile" onchange="uploadHandler(event)">

    <script src="https://code.jquery.com/jquery-3.3.1.min.js"></script>

    <script>
        function uploadHandler(e) {
            var files = e.target.files || e.dataTransfer.files;

            if (files && files.length > 0) {
                var file = files[0];

                resizeImage(file).then(function (result) {
                    return typeof result === 'string' ? convertToBlob(result, file.type) : result;
                }).then(function (blob) {
                    // 构建FormData
                    var formData = new FormData();
                    //注意：此处第3个参数最好传入一个带后缀名的文件名，否则很有可能被后台认为不是有效的图片文件
                    formData.append("file", blob, file.png); 
                    // 上传文件
                    $.ajax({
                        url: '/api/upload',
                        method: "POST",
                        data: formData,
                        cache: false,
                        processData: false,
                        contentType: false
                    }).then(function (res) {
                        console.log(res);
                    }).catch(function (err) {
                        console.log(err);
                    })
                });
            }
        }

        /**
         * 压缩裁剪图片
         */
        function resizeImage(file) {
            return new Promise(function (resolve, reject) {
                var reader = new FileReader();

                reader.onload = function () {
                    var img = new Image();

                    img.onload = function () {
                        var w = this.naturalWidth;
                        var h = this.naturalHeight;
                        var maxW = 500;
                        var maxH = 500;

                        // 如果图片尺寸小于最大限制，则不压缩直接上传
                        if (w <= maxW && h <= maxH) {
                            resolve(file);
                            return;
                        }

                        var level = 0.6;
                        var multiple = Math.max(w / maxW, h / maxH);
                        var resizeW = w / multiple;
                        var resizeH = h / multiple;

                        var canvas = document.createElement("canvas");

                        canvas.width = resizeW;
                        canvas.height = resizeH;

                        var ctx = canvas.getContext("2d");

                        ctx.drawImage(img, 0, 0, resizeW, resizeH);

                        var base64Img = canvas.toDataURL(file.type, level);
                        var arr = base64Img.split(",");

                        resolve(arr[1]);
                    };

                    img.src = this.result;
                };

                reader.readAsDataURL(file);
            });
        }

        /**
         * 将图片的base64字符串转换为Blob对象
         */
        function convertToBlob(base64Str, fileType) {
            var base64 = window.atob(base64Str);
            var len = base64.length;
            var buff = new ArrayBuffer(len);
            var uarr = new Uint8Array(buff);

            for (var i = 0; i < len; i++) {
                uarr[i] = base64.charCodeAt(i);
            }

            var blob = null;

            try {
                blob = new Blob([buff], { type: fileType });
            } catch (e) {
                var BlobBuilder = window.BlobBuilder = (
                    window.BlobBuilder ||
                    window.WebKitBlobBuilder ||
                    window.MozBlobBuilder ||
                    window.MSBlobBuilder
                );

                if (e.name === "TypeError" && BlobBuilder) {
                    var builder = new BlobBuilder();
                    builder.append(buff);
                    blob = builder.getBlob(fileType);
                }
            }

            return blob;
        }
    </script>
</body>

</html>
如何使用FormData上传压缩裁剪后的图片Blob对象

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