在浏览器中使用js-spark-md5计算文件的MD5

最近开发一个视频系统，用户需要把文件上传到服务器。服务器再上传到转码服务器，编码为m3u8格式。我觉得客户端可以直接上传到转码服务器。对转码服务器设置了跨域后，客户端可以直接上传视频文件，但是上传接口需要文件的MD5值，网上找了一个口碑极好的MD5库 js-spark-md5（据说性能是最牛逼的）

https://github.com/satazor/js-spark-md5

document.getElementById('file').addEventListener('change', function () {
    var blobSlice = File.prototype.slice || File.prototype.mozSlice || File.prototype.webkitSlice,
 file = this.files[0],
 chunkSize = 2097152, // Read in chunks of 2MB
 chunks = Math.ceil(file.size / chunkSize),
 currentChunk = 0,
 spark = new SparkMD5.ArrayBuffer(),
 fileReader = new FileReader();

    fileReader.onload = function (e) {
 console.log('read chunk nr', currentChunk + 1, 'of', chunks);
 spark.append(e.target.result);     // Append array buffer
 currentChunk++;

 if (currentChunk < chunks) {
     loadNext();
 } else {
     console.log('finished loading');
     console.info('computed hash', spark.end());  // Compute hash
 }
    };

    fileReader.onerror = function () {
 console.warn('oops, something went wrong.');
    };

    function loadNext() {
 var start = currentChunk * chunkSize,
     end = ((start + chunkSize) >= file.size) ? file.size : start + chunkSize;

 fileReader.readAsArrayBuffer(blobSlice.call(file, start, end));
    }

    loadNext();
});

// 分片大小，1Mb
const CHUNK_SIZE = 1024 * 1024;
// 文件
const file = ....;
// 文件大小
const size = file.size;
// 总分片数量
let totalChunk = Math.ceil(size / CHUNK_SIZE);
// spark  用于计算md5
const spark = new SparkMD5.ArrayBuffer(),

for (let i = 0; i < totalChunk; i ++){
	let start = i * CHUNK_SIZE;
    let end = ((start + CHUNK_SIZE) >= size) ? size : start + CHUNK_SIZE;
    // 分片的文件
    let chunk = file.slice(start, end);
    // 添加到spark
    spark.append(chunk);
}
// 计算出md5
const md5 = spark.end();

function md5(file, chunkSize) {
	return new Promise((resolve, reject) => {
		let blobSlice = File.prototype.slice || File.prototype.mozSlice || File.prototype.webkitSlice;
		let chunks = Math.ceil(file.size / chunkSize);
		let currentChunk = 0;
		let spark = new SparkMD5.ArrayBuffer();
		let fileReader = new FileReader();
	
		fileReader.onload = function(e) {
			spark.append(e.target.result); 
			currentChunk++;
			if (currentChunk < chunks) {
				loadNext();
			} else {
				let md5 = spark.end();
				resolve(md5);
			}
		};
	
		fileReader.onerror = function(e) {
			reject(e);
		};
	
		function loadNext() {
			let start = currentChunk * chunkSize;
			let end = start + chunkSize;
			if (end > file.size){
				end = file.size;
			}
			fileReader.readAsArrayBuffer(blobSlice.call(file, start, end));
		}
		loadNext();
	});
}