< QmlWeb‎ | Qml.js
Revision as of 16:02, 13 March 2015 by Akreuzkamp (talk | contribs)

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


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

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)

This page was last edited on 14 March 2015, at 15:37. Content is available under Creative Commons License SA 4.0 unless otherwise noted.