View source for QmlWeb/Qml.js/Design Questions and Decisions

This page intends to collect questions about software architecute and software design, pros and cons as well as the decisions made on the topic.

== Runtime Architecture ==
=== Getter/Setter Technique ===
Possibilities:
; Two methods getProperty(index) and setProperty(index, value):
* ''pro:'' super fast and memory efficient in all browsers (doesn't require closures or the like)
* ''con:'' not nice to read
* ''note:'' requires use of property indexes and a properties array (see below)
; C++ style getters and setters:
: ''this.width(); and this.setWidth(width);''
* ''note:'' C++ style
* ''pro:'' fast in all browsers
; Transparent getter/setter using Object.defineProperty
: ''Object.defineProperty(this, "width", { get function(){}, set: function(){} });''
* ''pro:'' nice while debugging
* ''con:'' worse performance in IE
* ''con:'' horrible performance in Firefox
; Transparent getter/setter using literal notation
* ''pro:'' nice while debugging
* ''con:'' worse performance in IE
* ''con:'' you can't use object literals and inheritance at the same time in a standard compliant manner


Benchmark: http://jsperf.com/getter-setter/7

'''Decision:''' Use getProperty and setProperty.

=== Storing properties ===
As we're using setters and getters in either way, we need to store the actual property value separated. There're multiple possibilities for that:
; Private member using closures
; Private member using like ''_width''
; Using property objects and direct object references
; Using property indexes and a properties array
* ''pro:'' If done right, it might provide weak references
; Using a properties object and access it per name
* ''con:'' Bad bad bad performance

Decision: Use property indexes and a properties array.

=== Handling bindings ===
; Let the bindings depend on each other and make them set the value on update
* ''pro:'' Seems logically like the right thing. After all it's the bindings that define the dependencies
* ''con:'' How to know when a property gets overwritten and thus the binding is invalidated?
; Let the properties depend on each other and make them reevaluate the binding when needed


=== Module Handling ===
The relevant point here is how to handle the case that in two different contexts, two different modules are loaded, which contain two different types with the same name.
The possibilities to handle that are:
; Always create a namespace, not only when imported with ''as''
* Makes generated code bigger and less readable
; Alternatives?

=== Possibly use a global pointer array to create weak references ===
* ''pro:'' As fast as a direct reference (within the limits of accuracy of the measurements)

=== Object properties ===
Some QML basic types, like color or QQuickAnchors, are object types and thus have properties themselves, like color.r or anchors.left. How to access/set their properties?