Using the Eval function.

The eval function is supposed to evaluate a mathmatical expression?

So if I have a text box and the user enters say 2+2 how would I code the eval function so it will return the result correctly.
I have been trying to do this but I can not get it to work correctly.

Thanks

var mathExpression = "2+2";
var mathAnswer;
mathAnswer = eval(mathExpression);
alert(mathAnswer);

get it?

I get it. Thanks