Multiconverter Javascript Program

Question

im trying to built a Multiconverter in javascript, but for some reason i can´t stop the loop, and i can´t get the result for the functions. i did the following:

    // conversion Dollars to Euros( 1USD = 0.892901) as of 11.08.2019; conversion Swiss Franc to Euro ( 1chf = 0.918063) as of 11-08-2019, conversion Knots to Kph (1knots = 1.85Kph);

    //Dollars to Euros

    function DollarstoEuros ( Dollars) { 
        return USD * 0.892901;
    }

    // Swiss Francs to Euros

    function SwissFrancsToEuros ( Francs ) {
        return Francs * 0.918063;
    }

    // Knots to Kph

    function KnotstoKph ( Knots ) {
        return Knots * 1.85;
    }

    // Ask the user which conversion they want to use
    function WhichConversion () {

    var answer = window.prompt( " Welcome to the Mutliconverter! What do you want to convert?  ( Dollars, Francs, Knots");
    if (answer == "Dollars", "Knots", "Francs"){
        return true;
    } else {
        return false;
    }
}

//Ask for a Value
function AskForValue () {
    var answer = window.prompt( " Enter a Value to Convert")
    return answer;
}

Should i change the function WhichConversion in order to separate the if answer? because the while and the var inside it seems ok to me, maybe or probably it´s a basic mistake, but im in my earlier steps in javascript, and apart of beeing similar, i prefer python.