Having trouble conceptualizing how i would change this if else statement into a switch statement

Question

I need assistance with changing a very long if/else if/else statement into a switch case statement. Conceptually im not certain of what should be put in the switch expression

if (!$jq('*').hasClass("answerPick")) {
    // if nothing is selected 
     finalURL= "productResults.aspx?N=1320325";
}
else if (q1 === undefined && q2 === undefined && q3Multi === undefined) {
    // if q1 a2 and q3 arent selected 
    finalURL= "productResults.aspx?N=1320325+" + q4Multi.join('+');
}
else if (q1 != undefined && q2 === undefined && q3Multi === undefined) {
    // if q1 a2 and q3 arent selected 
    finalURL= "productResults.aspx?N=1320325+" q15 + q4Multi.join('+');
}

else if (q1 === undefined && q2 === undefined) {
    // if q1 and q2 arent selected 
     finalURL= "productResults.aspx?N=1320325+" + q3Multi + q4Multi.join('+');
}
else if (q2 === undefined && q1 != undefined) {
    // if only q2 is left unselected 
      finalURL = "productResults.aspx?N=" + q15 + q3Multi + q4Multi.join('+');
}
else if (q2 === undefined && q3Multi === undefined) {
    // if only q1 is selected 
     finalURL = "productResults.aspx?N=" + q15;
}
else{
    // if everything is selected
      finalURL = "productResults.aspx?N=" + q2 + q3Multi + q4Multi.join('+');
}

---

switch(expression) {
  case n:
    code block
    break;
  case n:
    code block
    break;
  default:
    default code block
} 

Please let me know of anything else i should include. I think im missing something super obvious but conceptually it isnt clicking.

Answer 1

You can set a variable to a combination that indicates which variables are defined, and then switch on that.

if (!$jq('*').hasClass("answerPick")) {
    // if nothing is selected 
    finalURL= "productResults.aspx?N=1320325";
} else {
    var selected = (q1 === undefined ? "q1def" : "q1undef") + "+" + (q2 === undefined ? "q2def" : "q2undef") + "+" + (q3Multi === undefined ? "q3def" : "q3undef");
    switch(selected) {
    case "q1undef+q2undef+q3undef":
        // if q1 a2 and q3 arent selected 
        finalURL= "productResults.aspx?N=1320325+" + q4Multi.join('+');
        break;
    case "q1def+q2undef+q3undef":
        finalURL= "productResults.aspx?N=1320325+" q15 + q4Multi.join('+');
        break;
    case "q1undef+q2undef+q3def":
    case "q1undef+q2undef+q3undef":
        // if q1 and q2 arent selected 
        finalURL= "productResults.aspx?N=1320325+" + q3Multi + q4Multi.join('+');
        break;
    case "q1def+q2undef+q3def":
    case "q1def+q2undef+q3undef":
        // if only q2 is left unselected 
        finalURL = "productResults.aspx?N=" + q15 + q3Multi + q4Multi.join('+');
        break;
    case "q1def+q2undef+q3undef":
    case "q1undef+q2undef+q3undef":
        // if only q1 is selected 
        finalURL = "productResults.aspx?N=" + q15;
        break;
    default:
        // if everything is selected
        finalURL = "productResults.aspx?N=" + q2 + q3Multi + q4Multi.join('+');
        break;
    }
}