JS script to detect jpeg orientation from exif data using filereader api

jpeg-exif-image-orientation-js

var orientation = function (file, callback) {
    var fileReader = new FileReader();
    fileReader.onloadend = function () {
        var base64img = "data:" + file.type + ";base64," + _arrayBufferToBase64(fileReader.result);
        var scanner = new DataView(fileReader.result);
        var idx = 0;
        var value = 1; // Non-rotated is the default
        if (fileReader.result.length < 2 || scanner.getUint16(idx) != 0xFFD8) {
            // Not a JPEG
            if (callback) {
                callback(base64img, value);
            }
            return;
        }
        idx += 2;
        var maxBytes = scanner.byteLength;
        var littleEndian = false;
        while (idx < maxBytes - 2) {
            var uint16 = scanner.getUint16(idx, littleEndian);
            idx += 2;
            switch (uint16) {
                case 0xFFE1: // Start of EXIF
                    var endianNess = scanner.getUint16(idx + 8);
                    // II (0x4949) Indicates Intel format - Little Endian
                    // MM (0x4D4D) Indicates Motorola format - Big Endian
                    if (endianNess === 0x4949) {
                        littleEndian = true;
                    }
                    var exifLength = scanner.getUint16(idx, littleEndian);
                    maxBytes = exifLength - idx;
                    idx += 2;
                    break;
                case 0x0112: // Orientation tag
                    // Read the value, its 6 bytes further out
                    // See page 102 at the following URL
                    // http://www.kodak.com/global/plugins/acrobat/en/service/digCam/exifStandard2.pdf
                    value = scanner.getUint16(idx + 6, littleEndian);
                    maxBytes = 0; // Stop scanning
                    break;
            }
        }
        if (callback) {
            callback(base64img, value);
        }
    }
    fileReader.readAsArrayBuffer(file);
};