html5 filereader读取流注意事项

对于截取读入的文件，一定要new FileReader,不可写全局调用同一个reader.

错误代码！！！
function readAsBinaryString(file,callback){
    readrSpt();

    var part= 0,fileName=file.name,
        step=1024*10,start= 0, a=0,b= 0,total=file.size,loaded= 0,reader=new FileRead(),fileType=file.type;///这样写是错的，将导致reader流不在是同步读取

    //$("#fileLink").attr("href",URL.createObjectURL(blob));
    //将文件以arraybuffer形式读入
    (function(start){
        var blob=file.slice(start,start+step+1),self=arguments.callee;// console.log(blob)
        reader.readAsArrayBuffer(blob);
        reader.onprogress=function(e){
            loaded+=e.loaded;
            var per=loaded/total;
            if(loaded==total){
                per=100;
                callback(this.result,part,fileName,fileType,true);
            }else{
                per*=100;
                callback(this.result,part);
                part++;
            }
        }
        reader.onload=function(e){
            console.log(loaded)
            if(loaded<total){
                self(loaded);
                //  callback(this.result);
            }else{
                loaded=total;
            }
        }
    })(start);
}

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正确代码
function readAsBinaryString(file,callback){
    readrSpt();

    var part= 0,fileName=file.name,
        step=1024*10,start= 0, a=0,b= 0,total=file.size,loaded= 0,fileType=file.type;

    //$("#fileLink").attr("href",URL.createObjectURL(blob));
    //将文件以arraybuffer形式读入
    (function(start){
        var blob=file.slice(start,start+step+1),reader = new FileReader(),self=arguments.callee;
        // console.log(blob)
        reader.readAsArrayBuffer(blob);
        reader.onprogress=function(e){
            loaded+=e.loaded;
            var per=loaded/total;
            if(loaded==total){
                per=100;
                callback(this.result,part,fileName,fileType,true);
            }else{
                per*=100;
                callback(this.result,part);
                part++;
            }
        }
        reader.onload=function(e){
            console.log(loaded)
            if(loaded<total){
                self(loaded);
                //  callback(this.result);
            }else{
                loaded=total;
            }
        }
    })(start);
}

转载来源：http://www.cnblogs.com/tom-chang/p/4060650.html