SOURCE

var ImageTool = { /* * @param rawImageArray{ArrayBuffer|Array|Blob} */
    getSegments: function (rawImage, callback) {
        if (rawImage instanceof Blob) {
            var that = this;
            var fileReader = new FileReader();
            fileReader.onload = function () {
                that.getSegments(fileReader.result,
                    callback);
            };
            fileReader.readAsArrayBuffer(rawImage);
        } else {
            if (!rawImage.length && !rawImage.byteLength) {
                return [];
            }
            var head = 0,
                segments = [];
            var length, endPoint, seg;
            var arr = [].slice.call(new Uint8Array(rawImage), 0);
            while (1) {
                if (arr[head] === 0xff && arr[head + 1] === 0xda) { //Start of Scan 0xff 0xda SOS 
                    break;
                }
                if (arr[head] === 0xff && arr[head +
                    1] === 0xd8) { //Start of Image 0xff 0xd8 SOI 
                    head += 2;
                } else { //找到每个marker 
                    length = arr[head + 2] * 256 + arr[head + 3]; //每个marker 后 的两个字节为 该marker信息的长度 
                    endPoint = head + length + 2;
                    seg = arr.slice(head, endPoint); //截取信息 
                    head = endPoint;
                    segments.push(seg); //将每个marker + 信息 push 进去。 
                }
                if (head > arr.length) {
                    break;
                }
            }
            callback(segments);
        }
    },
    /* 
    * @param
    resizedImg {
        ArrayBuffer | Blob
    }* @param exifArr {
        Array | Uint8Array
    }*/
    insertEXIF: function (resizedImg, exifArr, callback) {
        if (resizedImg instanceof Blob) {
            var that = this;
            var fileReader = new FileReader();
            fileReader.onload = function () {
                that.insertEXIF(fileReader.result,
                    exifArr, callback);
            };
            fileReader.readAsArrayBuffer(resizedImg);
        } else {
            var arr = [].slice.call(new Uint8Array(resizedImg),
                0);
            if (arr[2] !== 0xff || arr[3] !== 0xe0) { // throw new Error("Couldn't find APP0 marker from resized image data.");
                return resizedImg; //不是标准的JPEG文件 
            }
            var app0_length = arr[4] * 256 + arr[5]; //两个字节 
            var newImage = [0xff, 0xd8].concat(exifArr, arr.slice(4 +
                app0_length)); //合并文件 SOI + EXIF + 去除APP0的图像信息 
            callback(new Uint8Array(newImage));
        }
    },

    getEXIF: function (segments) {
        if (!segments.length) {
            return [];
        }
        var seg = [];
        for (var x = 0; x < segments.length; x++) {
            var s = segments[x]; //TODO segments 
            if (s[0] === 0xff && s[1] === 0xe1) { // app1 exif 0xff 0xe1 seg=s eg.concat(s);
            }
        }
        return seg;
    },
    decode64: function (base64) {
        var b64 = "data:image/jpeg;base64,";
        if (base64.slice(0,
            23) !== b64) {
            return [];
        }
        var binStr = window.atob(base64.replace(b64, ""));
        var buf = new Uint8Array(binStr.length);
        for (var i = 0, len = binStr.length; i < len; i++) {
            buf[i] = binStr.charCodeAt(i);
        }
        return buf;
    },
    /* *@param arr{Array} */
    encode64: function (arr) {
        var data = "";
        for (var i = 0, len = arr.length; i < len; i++) {
            data += String.fromCharCode(arr[i]);
        }
        return "data:image/jpeg;base64," + window.btoa(data);
    }
};
var filedom = document.getElementById("filedom");
var imgdom = document.getElementById("img");
var btn = document.getElementById("btn");
btn.onclick = function () {
    console.log('filedom: ', filedom);
    var imgFile = filedom.files[0];
    if (!imgFile) {
        alert("请选择图片文件！");
        return false;
    }
    showImage(imgFile, function (src) {
        imgdom.src = src;
        imgdom.onload = function () {
            imageResize(imgdom, 400, 225, 1, function (blob) {
                ImageTool.getSegments(imgFile, function (segments) {
                    var exif = ImageTool.getEXIF(segments); //获取exif信息 
                    ImageTool.insertEXIF(blob, exif, function (newImage) {
                        showImage(new Blob([newImage], {
                            type: "image/jpeg"
                        }),
                            function (src) {
                                var img = new Image();
                                img.src = src;
                                document.body.appendChild(img);
                            });
                    });
                }); //获取 分割segments

            });
        }
    });
}

function showImage(file, callback) {
    var reader = new FileReader();
    reader.onload = function () {
        callback(reader.result);
    }
    reader.readAsDataURL(file);
}

function imageResize(img, width, height, quality, callback) {
    var type = "image/jpeg";
    var
        canvas = document.createElement("canvas"),
        ctx = canvas.getContext("2d"); // quality = options.quality || 0.8; 
    canvas.width = width;
    canvas.height = height;
    ctx.drawImage(img, 0, 0, width, height);
    canvas.toBlob(callback, type, quality);
}

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

<head>
    <meta charset="utf-8">
    <style>
    </style>

</head>

<body>

    <div>
        <input type="file" id="filedom" />
        <img src="#" width="200" id="img">
        <br>
        <button id="btn">获取</button>
    </div>

</body>

</html>