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.g or anchors.left. How to access/set their properties?