Question

我想从嵌套函数（var hash）中获取值，但返回不起作用。我已经读过我的问题是我不能在异步函数中使用return而我应该使用promises，经过一些研究后我发现promises会产生一些compatibility problem with browsers。所以我正在寻找一种简单的方法来获得我的结果。

此函数用于通过SPARKMD5

获取MD5哈希值

 function calcmd5(file) {

        var blobSlice = File.prototype.slice || File.prototype.mozSlice || File.prototype.webkitSlice,
            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');
                var hash = spark.end();
                console.log( hash );
                return hash; // I want this result
                //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();        
    }

    var result = calcmd5(file); // use to get the hash

无法在异步函数中使用return

0 个答案: