The top-level function, eval, evaluates and/or executes a string
First, eval determines if the argument is a valid string and
statements in the code, they will be executed and eval will return
the value of the last statement (if there is a value). If there is a
Note that the codestring argument is optional. However,
if there is no argument, eval returned, "undefined".
eval("fred=999; wilma=777; document.write(fred + wilma);");