js自建readAsBinaryString方法

if (typeof(FileReader.prototype.readAsBinaryString) !== "function") {
    FileReader.prototype.readAsBinaryString = function (fileData) {
        var binary = "";
        var pt = this;
        var reader = new FileReader();
        reader.onload = function (e) {
            var bytes = new Uint8Array(reader.result);
            var length = bytes.byteLength;
            for (var i = 0; i < length; i++) {
                binary += String.fromCharCode(bytes[i]);
            }
            var obj = {};
            obj.target = {result: binary};
            pt.onload(obj);
        }
        reader.readAsArrayBuffer(fileData);
    }
}