inheritance.md

Class Inheritance & Overloading

If we want to change basic behaviour about how our data is stored in JSONifier, inheritance is a good way to go about this.

Example

I want to store JSON objects that are particular to URL path. We can achieve this by munging the namespaces, but I'd prefer to have a clearly defined API for my users.

The key things to modify are our constructor and the state getters and setters:

class ThePath extends JSONifier {
    constructor(state, ops) {
        super(state, ops);
        this.__state = {};

        // Use old path to sherpa in inherited data
        this.path = this.path  || '/';
        this.state = this.__tmp;
        // Use new path for all that follows
        this.path = ops ? ops.path || '/' : '/';
    }

    get state() {
        return this.path
            ? this.__state[this.path]
            : this.__tmp
            ;
    }

    set state(s) {
        return this.path
            ? this.__state[this.path] = s
            : this.__tmp = s
            ;
    }

    build(path) {
        this.path = path || '/';
        return super.build();
    }
}

So our new API is quite exciting, we can now inherit data for multiple paths, but restrict to a particular path at build time:

let base = new ThePath({path: '/login'})
    .add({
        'username', 'blakef'
        'attempts', function* mockAttempts() { let count = 0; while(true) yield ++count; }
    });

let fin = new ThePath({path: '/authenticated'})
    .add({ 'message': 'welcome user'});

> fin.build('/login').next().value
{ 'username': 'blakef', 'attempts': 0 }

> fin.build('/authenticated').next().value
{ 'message': 'welcome user' }

So we're able to gradually build up more complexity, but still remain concise.