How to load a CSV file and then convert it into a javascript array (Compare input of form with external csv file to display specific content)

I'm new to javascript but this is what I've pieced together from here and w3schools.
Apologies if something similar already exists.

I want to create a page where people with a 6-character code can find out what they've won.

In my example;
I have 5 toy cars and 5 rubber duckies to give away.
(codes will eventually by randomised)
If I was to upscale this to 500 toy cars and 500 rubber duckies I believe there has to be a better way than what I have created. (below)

Is there a way to compare the input with a csv file (or other file type located online) that I can use to validate the if/else statements in
"function compareinput()" ?

I'd prefer javascript solution as opposed to PHP.

See fiddle here; https://jsfiddle.net/tn5Lp3mc/
(apologies in advanced for not compartmentalising my code, I don't know how to use jsfiddle)

function compareinput() {
var x = document.getElementById("forminput");
var text = "";
var i;
var varbl;
for (i = 0; i < x.length ;i++) {
text += x.elements[i].value + "<br>";
}

varbl = text.toUpperCase().substring(0, 6);

if (varbl == "RD1234" ||
varbl == "RD4567" ||
varbl == "RD7894" ||
varbl == "RD8454" ||
varbl == "RD9854") {
displayRubberduck ();
}
else if (varbl == "TC5678" ||
varbl == "TC1234" ||
varbl == "TC9874" ||
varbl == "TC8989" ||
varbl == "TC1212") {
displayToycar ();
}
else {
displayInvalidcode();
}


}

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