字節byte自適應轉換為B、KB、MB、GB、TB

change(limit){
    var size = "";
    if(limit < 0.1 * 1024){ //小於0.1KB，則轉化成B
        size = limit.toFixed(2) + "B"
    }else if(limit < 0.1 * 1024 * 1024){ //小於0.1MB，則轉化成KB
        size = (limit/1024).toFixed(2) + "KB"
    }else if(limit < 0.1 * 1024 * 1024 * 1024){ //小於0.1GB，則轉化成MB
        size = (limit/(1024 * 1024)).toFixed(2) + "MB"
    }else{ //其他轉化成GB
        size = (limit/(1024 * 1024 * 1024)).toFixed(2) + "GB"
    }

    var sizeStr = size + ""; //轉成字符串
    var index = sizeStr.indexOf("."); //獲取小數點處的索引
    var dou = sizeStr.substr(index + 1 ,2) //獲取小數點后兩位的值
    if(dou == "00"){ //判斷后兩位是否為00，如果是則刪除00
        return sizeStr.substring(0, index) + sizeStr.substr(index + 3, 2)
    }
    return size;
}