const Exif = {};
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Exif.getData = (img) => new Promise((reslove, reject) => {
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let obj = {};
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getImageData(img).then(data => {
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obj.arrayBuffer = data;
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obj.orientation = getOrientation(data);
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reslove(obj)
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}).catch(error => {
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reject(error)
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})
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})
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// 这里的获取exif要将图片转ArrayBuffer对象，这里假设获取了图片的baes64
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// 步骤一
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// base64转ArrayBuffer对象
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function getImageData(img) {
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let data = null;
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return new Promise((reslove, reject) => {
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if (img.src) {
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if (/^data\:/i.test(img.src)) { // Data URI
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data = base64ToArrayBuffer(img.src);
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reslove(data)
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} else if (/^blob\:/i.test(img.src)) { // Object URL
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var fileReader = new FileReader();
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fileReader.onload = function (e) {
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data = e.target.result;
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reslove(data)
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};
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objectURLToBlob(img.src, function (blob) {
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fileReader.readAsArrayBuffer(blob);
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});
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} else {
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var http = new XMLHttpRequest();
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http.onload = function () {
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if (this.status == 200 || this.status === 0) {
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data = http.response
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reslove(data)
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} else {
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throw "Could not load image";
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}
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http = null;
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};
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http.open("GET", img.src, true);
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http.responseType = "arraybuffer";
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http.send(null);
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}
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} else {
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reject('img error')
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}
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})
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}
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function objectURLToBlob(url, callback) {
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var http = new XMLHttpRequest();
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http.open("GET", url, true);
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http.responseType = "blob";
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http.onload = function (e) {
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if (this.status == 200 || this.status === 0) {
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callback(this.response);
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}
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};
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http.send();
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}
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function base64ToArrayBuffer(base64) {
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base64 = base64.replace(/^data\:([^\;]+)\;base64,/gmi, '');
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var binary = atob(base64);
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var len = binary.length;
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var buffer = new ArrayBuffer(len);
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var view = new Uint8Array(buffer);
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for (var i = 0; i < len; i++) {
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view[i] = binary.charCodeAt(i);
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}
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return buffer;
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}
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// 步骤二，Unicode码转字符串
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// ArrayBuffer对象 Unicode码转字符串
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function getStringFromCharCode(dataView, start, length) {
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var str = '';
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var i;
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for (i = start, length += start; i < length; i++) {
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str += String.fromCharCode(dataView.getUint8(i));
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}
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return str;
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}
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// 步骤三，获取jpg图片的exif的角度（在ios体现最明显）
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function getOrientation(arrayBuffer) {
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var dataView = new DataView(arrayBuffer);
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var length = dataView.byteLength;
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var orientation;
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var exifIDCode;
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var tiffOffset;
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var firstIFDOffset;
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var littleEndian;
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var endianness;
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var app1Start;
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var ifdStart;
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var offset;
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var i;
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// Only handle JPEG image (start by 0xFFD8)
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if (dataView.getUint8(0) === 0xFF && dataView.getUint8(1) === 0xD8) {
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offset = 2;
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while (offset < length) {
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if (dataView.getUint8(offset) === 0xFF && dataView.getUint8(offset + 1) === 0xE1) {
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app1Start = offset;
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break;
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}
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offset++;
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}
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}
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if (app1Start) {
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exifIDCode = app1Start + 4;
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tiffOffset = app1Start + 10;
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if (getStringFromCharCode(dataView, exifIDCode, 4) === 'Exif') {
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endianness = dataView.getUint16(tiffOffset);
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littleEndian = endianness === 0x4949;
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if (littleEndian || endianness === 0x4D4D /* bigEndian */) {
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if (dataView.getUint16(tiffOffset + 2, littleEndian) === 0x002A) {
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firstIFDOffset = dataView.getUint32(tiffOffset + 4, littleEndian);
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if (firstIFDOffset >= 0x00000008) {
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ifdStart = tiffOffset + firstIFDOffset;
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}
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}
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}
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}
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}
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if (ifdStart) {
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length = dataView.getUint16(ifdStart, littleEndian);
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for (i = 0; i < length; i++) {
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offset = ifdStart + i * 12 + 2;
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if (dataView.getUint16(offset, littleEndian) === 0x0112 /* Orientation */) {
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// 8 is the offset of the current tag's value
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offset += 8;
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// Get the original orientation value
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orientation = dataView.getUint16(offset, littleEndian);
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// Override the orientation with its default value for Safari (#120)
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// if (IS_SAFARI_OR_UIWEBVIEW) {
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// dataView.setUint16(offset, 1, littleEndian);
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// }
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break;
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}
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}
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}
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return orientation;
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}
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export default Exif
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