我有一个功能，用户可以导出数据库信息。但是，如果用户选择要导出的所有选项，则需要1分钟或更长时间才能下载.csv文件。我只包括if语句的一部分，我在那里提取所有数据。
这里是：
function exportTheData() {
//get the data for data array
if(exportVolumeData == 1) {
for(j=0; j<plantData1.length; j++) {
i = plantData["MergeKey_lvl00"].indexOf(plantData1["MergeKey_lvl00"][j]);
data.push(plantData["PlantName"][i]);
if(statesExport == 1) {
countyindex = counties["CountyId"].indexOf(plantData["LocationId"][i]);
stateid = counties["StateId"][countyindex];
statename = states["StateName"][states["StateId"].indexOf(stateid)];
data.push(statename);
}
if(countyExport == 1) {
countyindex = counties["CountyId"].indexOf(plantData["LocationId"][i]);
countyname = counties["CountyName"][countyindex];
data.push(countyname);
}
if(basinsExport == 1) {
countyindex = counties["CountyId"].indexOf(plantData["LocationId"][i]);
subbasinid = counties["SubBasinId"][countyindex];
subbasinindex = basinSub["SubBasinId"].indexOf(subbasinid);
basinid = basinSub["BasinId"][subbasinindex];
basinindex = basin["BasinId"].indexOf(basinid);
basinname = basin["BasinName"][basinindex];
data.push(basinname);
}
if(subBasinsExport == 1) {
countyindex = counties["CountyId"].indexOf(plantData["LocationId"][i]);
subbasinid = counties["SubBasinId"][countyindex];
subbasinindex = basinSub["SubBasinId"].indexOf(subbasinid);
subbasinname = basinSub["SubBasinName"][subbasinindex];
data.push(subbasinname);
}
if(paddsExport == 1) {
countyindex = counties["CountyId"].indexOf(plantData["LocationId"][i]);
subpaddid = counties["SubPaddId"][countyindex];
subpaddindex = paddSub["SubPaddId"].indexOf(subpaddid);
paddid = paddSub["PaddId"][subpaddindex];
paddindex = padd["PaddId"].indexOf(paddid);
paddname = padd["PaddName"][paddindex];
data.push(paddname);
}
if(subPaddsExport == 1) {
countyindex = counties["CountyId"].indexOf(plantData["LocationId"][i]);
subpaddid = counties["SubPaddId"][countyindex];
subpaddname = paddSub["SubPaddName"][paddSub["SubPaddId"].indexOf(subpaddid)];
data.push(subpaddname);
}
if(fullNameExport == 1) {
companyindex = getCompanyInfo["MergeKey_lvl00"].indexOf(plantData["OperatorId"][i]);
fullname = getCompanyInfo["FullName"][companyindex];
data.push(fullname);
}
if(shortNameExport == 1) {
companyindex = getCompanyInfo["MergeKey_lvl00"].indexOf(plantData["OperatorId"][i]);
shortname = getCompanyInfo["ShortName"][companyindex];
data.push(shortname);
}
if(tickerExport == 1) {
companyindex = getCompanyInfo["MergeKey_lvl00"].indexOf(plantData["OperatorId"][i]);
ticker = getCompanyInfo["Ticker"][companyindex];
data.push(ticker);
}
volumeindex = plantData1["MergeKey_lvl00"].indexOf(plantData["MergeKey_lvl00"][i]);
startdate = plantData1["MonthStartDate"][volumeindex];
volumetypeindex = plantData2["VolumeTypeId"].indexOf(plantData1["VolumeTypeId"][j]);
volumetype = plantData2["VolumeType"][volumetypeindex];
volumeunit = plantData2["Unit"][volumetypeindex];
volume = plantData1["Volume"][volumeindex];
data.push(startdate);
data.push(volumetype);
data.push(volumeunit);
data.push(volume);
}
/* * Convert our data to CSV string */
var CSVString = prepCSVRow(titles, titles.length, '');
CSVString = prepCSVRow(data, titles.length, CSVString);
/* * Make CSV downloadable*/
var downloadLink = document.createElement("a");
var blob = new Blob(["\ufeff", CSVString]);
var url = URL.createObjectURL(blob);
downloadLink.href = url;
downloadLink.download = "data.csv";
/** Actually download CSV */
document.body.appendChild(downloadLink);
downloadLink.click();
document.body.removeChild(downloadLink);
}
这是我将数据数组转换为csv string的地方：
function prepCSVRow(arr, columnCount, initial) {
var row = ''; // this will hold data
var delimeter = ','; // data slice separator, in excel it's `;`, in usual CSv it's `,`
var newLine = '\r\n'; // newline separator for CSV row
/* * Convert [1,2,3,4] into [[1,2], [3,4]] while count is 2
* @param _arr {Array} - the actual array to split
* @param _count {Number} - the amount to split
* return {Array} - splitted array */
function splitArray(_arr, _count) {
var splitted = [];
var result = [];
_arr.forEach(function(item, idx) {
if ((idx + 1) % _count === 0) {
splitted.push('"' + item + '"');
result.push(splitted);
splitted = [];
} else {
splitted.push('"' + item + '"');
}
});
return result;
}
var plainArr = splitArray(arr, columnCount);
// don't know how to explain this
// you just have to like follow the code
// and you understand, it's pretty simple
// it converts `['a', 'b', 'c']` to `a,b,c` string
plainArr.forEach(function(arrItem) {
arrItem.forEach(function(item, idx) {
row += item + ((idx + 1) === arrItem.length ? '' : delimeter);
});
row += newLine;
});
return initial + row;
}
关于如何加快速度的任何想法？我们在数据库中有超过6,000行数据。谢谢！
答案 0 :(得分：1)
将data.push ..更改为data [data.length] = ..使功能更快。另外，我为countyindex和companyindex创建了变量，而不是在同一个函数中多次调用它。
此外，清理功能的最后部分确实有帮助：
/* * Convert our data to CSV string */
var CSVString = prepCSVRow(titles, titles.length);
CSVString += prepCSVRow(data, titles.length);
/* * Make CSV downloadable*/
var downloadLink = document.createElement('a'),
blob = new Blob(['\ufeff', CSVString]);
downloadLink.href = URL.createObjectURL(blob);
downloadLink.download = 'data.csv';
/** Actually download CSV */
document.body.appendChild(downloadLink);
downloadLink.click();
document.body.removeChild(downloadLink);