How to handle large amount of data in Excel Web AddIn (task pane)

I've created an Excel Web AddIn (task pane)

I have a dataset of 500,000 rows. When I use javascript it hangs. How can I quickly store the data and retrieve?

function getValue(strA, strB){

	if (strA == "aa" && strB == "bb") {return 82;}
	if (strA == "bb" && strB == "aa") {return 82;}

	if (strA == "cc" && strB == "dd") {return 83;}
	if (strA == "dd" && strB == "cc") {return 83;}

	if (strA == "ee" && strB == "dd") {return 85;}
	if (strA == "dd" && strB == "ee") {return 85;}

	if (strA == "ff" && strB == "bb") { return 90; }
	if (strA == "bb" && strB == "ff") { return 90; }

}