Optimize the functions in javascript

If we have the function:

function test(a,b){
    return a + b;
}

and we launch test(1,2) we will get 3 as a result.
If this function is for example inside a loop which could execute it again with the exact same parameters (i.e. test(1,2)) always obtaining the same result (3), we will have executed a function uselessly because it has already been launched previously, therefore, using computing power for nothing.

While doing:

var of=new optimizeFunction();
for(var i=0;i<10;i++)
    console.log(of.exec("test",[1,2]));

we will always have the result 3 but the function will be executed only once and the value stored, at subsequent uses the value in memory will be shown without re-executing the function.

In case we had the function:

function test(a,b){
    return a + b + global_variable;
}

we will use the object like this:

of.exec("test", [1, 2], [global_variable]);

Here is the code of optimizeFunction

function optimizeFunction(){
    this.memory={};
    var self=this;
    this.name_gen=function(ar){
        return ar[0]+JSON.stringify(ar[1])+JSON.stringify(ar[2]);
    }
    this.exec=function(func_name,func_arg,func_arg_external){
        var name = self.name_gen(arguments);
        if(typeof self.memory[name] === "undefined"){
            var args=JSON.stringify(func_arg).replace("[","").replace("]","");
            self.memory[name] = eval(func_name+'('+args+');');
        }
        return self.memory[name];
    }
}