Looking for a better solution than a bunch of switch statements in my JavaScript

Question

I'm calling this function from my html (and in some cases from another function in my JavaScript). These type of switch statements are starting to litter my code. Is there a more elegant solution to these if statements? I wish I could pass a reference to the variables I want to modify. I'm finally asking the question because now I have a situation where if I do it this same way, I'm going to have an ugly switch statement with hundreds of cases which I'm guessing not only looks ugly, but will hurt performance.

function incCriteriaStats(exp){
    switch (exp) {
      case "a":
        numOfA++;
        break;
      case "b":
        numOfB++;
        break;
      case "c":
        numOfC++;
        break;
      case "d":
        numOfD++;
        break;
      case "e":
        numOfE++;
        break;
      case "f":
        numOfF++;
        break;
      case "g":
        numOfG++;
        break;    
    }
|

Answer 1

Why not use an object to store the values for a, b, c, etc, rather than using separate numOfA, numOfB, etc variables:

var obj = { 
   "a": 0,
   "b": 0,
   "c": 0,
   "d": 0,
   "e": 0,
   "f": 0,
   "g": 0
};

This will allow you to do something nice and simple like this:

function incCriteriaStats(exp){
   if (obj[exp] != null)
       obj[exp]++;
}

Answer 2

Use an object, with the keys being the letters, and then you can just do:

function incCriteriaStats(exp) {
        if(exp in obj)
             obj[exp]++;
}

Answer 3

var obj={};
function incCriteriaStats(exp) {
    if (typeof(obj[exp]=="undefined") {
        obj[exp]=1;
    } else {
        obj[exp]++;
    }
}

The object obj will end up like:

{
    "a": 4,
    "b": 5,
    ...
}

Answer 4

Obj isn't accessible from global scope, you can only get it by calling incCriteriaStats which increment key exp in obj var and return it

var incCriteriaStats = (function( ) {
        var obj={}
        return function( exp ) { 
          exp ? obj[ exp ] = ( obj[ exp ] || 0 ) +1 : 0;
          return obj;
        }
     })();

incCriteriaStats( "a" )
incCriteriaStats( "a" )
incCriteriaStats( "a" )[ "a" ] // 3
incCriteriaStats( "a" )[ "a" ] // 4
incCriteriaStats( "b" );

var obj = incCriteriaStats() // get the `obj` from inside incCriteriaStatus without modifying it;
obj.a == 4; //true
obj.b == 1; //true