Feature Request: Default values for parameters of events and functions

Easier to show rather explain:
```js
on reset(count = #words.children.length)
```
```js
def nextWord(value = '')
```
If the event property wasn't set, then allow an expression to be evaluated for the default value of that property. Similarly, if an argument wasn't passed in, allow an expression to be evaluated for the default value of that argument to a function. I'm suggesting the `=` syntax, but other words may make sense as well (such as `default`). Note that this may be complicated once multiple arguments are concerned, such as
```js
def nextWord(value = '', value2, value3 = 5)
```