@gamestdio/state-listener

Deeply compare JavaScript objects and listen to changes. Used in colyseus.js

Usage

This library is meant for listening to changes in a JavaScript object.

import { StateContainer } from "@gamestdio/state-listener"

// Create the container instance.
let container = new StateContainer({
    entities: {
        one: { x: 10, y: 10 }
    }
});

Listening to changes

container.listen("entities/:id/:attribute", (change: DataChange) => {
    console.log(change.path.id, change.path.attribute, change.operation, change.value);
});

// Setting new data into the container will trigger the matching listeners
container.set({ entities: { one: { x: 20 } } });

// Console output
// => "one", "x", "replace", 20
// => "one", "y", "remove", undefined

On this example, two properties has been changed ("entities/one/x", and "entities/one/y"). Thus, the callback will be triggered twice.

Fallback listener

You can use a fallback listener when you're not sure how exactly the change will come. Useful during development process.

Please note that change.path in the fallback listener will be an array containing the full path to the property that has changed.

container.listen((change: DataChange) => {
    console.log(change.path, change.operation, change.value);
})

// Setting new data into the container will trigger the matching listeners
container.set({ entities: { one: { x: 20 } } });

// Console output
// => ["entities", "one", "x"], "replace", 20
// => ["entities", "one", "y"], "remove", undefined

See tests for more usage examples.

Registering custom placeholders

Registering the placeholder:

container.registerPlaceholder(":xyz", /([xyz])/);

Using the matcher:

container.listen("entity/:id/:xyz", (change: DataChange) => {
    myEntities[ change.path.id ][ change.path.xyz ] = change.value;
});

Built-in placeholders

• :id: /([a-zA-Z0-9\-_]+)/
• :number: /([0-9]+)/
• :string: /(\w+)/
• :axis: /^([xyz])$/
• :*: /(.*)/

When any other name is used starting with : (e.g. :example), * will be used by default.

Inspiration

The compare method is highly based on fast-json-patch implementation.

License

MIT