One time computation

gistfile1.js

    function getQueryParams(param) {

        var qs = document.location.search.split("+").join(" "),
            params = {},
            tokens,
            re = /[?&]?([^=]+)=([^&]*)/g;

        while (tokens = re.exec(qs)) {
            params[decodeURIComponent(tokens[1])] = decodeURIComponent(tokens[2]);
        } 

        // redefine this function with a closure around the computed params
        getQueryParams = function(param){
            return params[param];
        };

        return params[param];
    }

// one time computation / init pattern
function myFunc(arg){
   
   var obj = {};

   /*
   	insert one time computation
   */

   // redefine myFunc with closure around arg and obj
   myFunc = function(arg){
       return obj[arg];
   }

}

// can then be used like this

myFunc('arg1'); // runs one time computation block
myFunc('arg2'); // should not run one time comptutation block but still return a result

Is this the best to have a helper function run some one time computation? Basically it runs some setup and then redefines itself with a closure around the computer variables.