字节byte自适应转换为B、KB、MB、GB、TB

change(limit){
    var size = "";
    if(limit < 0.1 * 1024){ //小于0.1KB，则转化成B
        size = limit.toFixed(2) + "B"
    }else if(limit < 0.1 * 1024 * 1024){ //小于0.1MB，则转化成KB
        size = (limit/1024).toFixed(2) + "KB"
    }else if(limit < 0.1 * 1024 * 1024 * 1024){ //小于0.1GB，则转化成MB
        size = (limit/(1024 * 1024)).toFixed(2) + "MB"
    }else{ //其他转化成GB
        size = (limit/(1024 * 1024 * 1024)).toFixed(2) + "GB"
    }

    var sizeStr = size + ""; //转成字符串
    var index = sizeStr.indexOf("."); //获取小数点处的索引
    var dou = sizeStr.substr(index + 1 ,2) //获取小数点后两位的值
    if(dou == "00"){ //判断后两位是否为00，如果是则删除00
        return sizeStr.substring(0, index) + sizeStr.substr(index + 3, 2)
    }
    return size;
}