I have many classes that has the following form.
static defaultInstance() {
if (!defaultInstance) {
defaultInstance = new Child1()
}
return defaultInstance
}
Since they have a common base class, I wanted to add the common function to the base class, but don't know how.
(having trouble with new Child1())
If Child1 is supposed to refer to the "current" class, i.e. the class that defaultInstance is invoked on, then you can just do
defaultInstance = new this();
This follows the normal JavaScript rules: If you invoke the function with Child1.defaultInstance(), then this refers to Child1.
However, this probably doesn't do what you want. If you define defaultInstance on the base class, then all child classes share the same defaultInstance variable.
If you want to have an instance per class, then each class needs its own defaultInstance method, or you need to use a property instead, e.g.
if (!this.__defaultInstance) {
this.__defaultInstance = new this();
}
Map instead of __defaultInstance? Also that would need to be this.hasOwnProperty('__defaultInstance') or the class inheritance could break it.
class name -> instance map? That would work too. Or maybe a WeakMap.map.set(this, new this());. Good call that WeakMap probably makes more sense, though unless you're dynamically declaring subclasses, the Map will probably be relatively static.
__defaultInstance is a static member variable and each class has its own __defaultInstance ? I guess map variable could live in someplace where all classes can access/share.