308297 - DOM methods can't have optional/default arguments in JS

Status: RESOLVED INVALID

(Core :: DOM: Core & HTML, defect)

Description

[Yuh-Ruey Chen]

User-Agent:       Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8b4) Gecko/20050908 Firefox/1.4
Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8b4) Gecko/20050908 Firefox/1.4

Some DOM methods are very convoluted and some arguments to those methods should
be optional. Examples:

addEventListener: useCapture argument should default to false
cloneNode: argument should be default to false
init*Event (initMouseEvent being by far the worst)
much of the XPath DOM methods

I'm sure there has to be an existing bug concerning this, but for the life of me
I can't find it (searched "optional arg", "optional param", "default arg",
"default param", and "not enough arg"). Closest entry I could find is bug
125497, but I'm not sure if that's related. However, the bug description says
something very relevant to this subject:

"optional parameters truly are 
useful: in our experience they are much more intuitive to JavaScript 
programmers than other solutions (passing null, or calling different 
functions), and they allow for some degree of method overloading"

So why are there no optional/default parameters for DOM methods? Is it a
technical limitation? Or is it because of a strict interpretation of the W3C
specs? If it's the latter, then why are JS functions valid EventListener's when
an EventListener is supposed to be an object containing a handleEvent method?
This seems very inconsistent to me in terms of JS convenience.

Reproducible: Always

Steps to Reproduce:

Comment 1

[Peter Van der Beken [:peterv]]

(In reply to comment #0)
> So why are there no optional/default parameters for DOM methods? Is it a
> technical limitation? Or is it because of a strict interpretation of the W3C
> specs?

The latter.

> If it's the latter, then why are JS functions valid EventListener's when
> an EventListener is supposed to be an object containing a handleEvent method?

Because that's what the DOM Spec specifies in the EcmaScript binding. See
http://www.w3.org/TR/2000/REC-DOM-Level-2-Events-20001113/ecma-script-binding.html

I vote for WONTFIX.

Comment 2

[Dave Townsend [:mossop]]

The DOM is a standard and we follow it. It does not specify any optional arguments.

JS functions are valid event listeners because the DOM spec says the following:

Object EventListener
    This is an ECMAScript function reference. This method has no return value.
The parameter is a Event object.

I suspect this is INVALID or WONTFIX

Comment 3

[Yuh-Ruey Chen]

Alright, I understand strictly following the spec and I now see the
EventListener JS binding, though I still disagree with the strictness.

IMO there should be the following set of rules for a JS binding to the DOM:
1) a JS function implements any interface that contains a single method and only
that method
2) any interface that has a method that accepts an array index and only one such
method should be indexable via the bracket notation (e.g. NodeList objects can
already by indexed)
3) arguments that accept values of false, null, or "" should be optional unless
there is a later argument that doesn't accept those values
4) a group of properties that function as a pseudo-union (only one property has
a meaningful value at a time) should somehow be condensed into a single property
for JS

Comment 4

[Dave Townsend [:mossop]]

(In reply to comment #3)
> IMO there should be the following set of rules for a JS binding to the DOM:

It's not up to us to decide on a set of rules for a JS binding to the DOM. The
W3C have already defined a JS binding to the DOM and that is the standard that
all browsers should work to.