javascript - pre-defined parameters

I want to be able to do this in JavaScript:

function myFunction(one, two = 1) {
     // code

}

myFunction("foo", "2");

myFunction("bar");

I tried this and it doesn't work. I don't know how to call this type of parameters, could somebody point me in the right direction?

Thanks.

Answer

function foo(a, b)
 {
   a = typeof a !== 'undefined' ? a : 42;
   b = typeof b !== 'undefined' ? b : 'default_b';
   //...
 }

Possibly duplicate of Set a default parameter value for a JavaScript function