Custom Component

Kaboom uses a flexible component system that helps you compose game logic.

Let's take a look at how the default component lifespan() is implemented.

function lifespan(time) {
    let timer = 0;
    return {
        id: "lifespan",
        update() {
            timer -= dt();
            if (timer <= 0) {
                destroy(this);
            }
        },
    };
}

Components are just plain functions that returns an object. The return object will contain all the exposed states, methods, and event hooks of the component. In this case, the lifespan() component returns an id, which is a string which serves as an unique identification of the comp. There's also an update(), which is an event hook that'll run every frame. All this inside the component functions refer to the game obj it's attached to.

All special fields:

function mycomp() {
    // use closed local variable for internal data
    let data = 123;
    return {
        id: "mycomp",
        // if this comp requires other comps to work
        require: [ "area", "pos", ],
        // runs when the obj is added to scene
        add() {
            debug.log("Hi! This should only be fire once.");
        },
        // runs every frame
        update() {
            // we're using a method from "pos" comp here, so we declare require "pos" above
            this.move(200, 0);
        },
        // runs every frame, after update
        draw() {
            drawLine(this.pos, mousePos());
        },
        // runs when obj is destroyed
        destroy() {
            debug.log("Oh bye");
        },
        // what to display in inspect mode
        inspect() {
            return "some state that deserves to be shown in inspect mode";
        },
    }
}

Most kaboom built-in components are built using public interfaces, feel free to check them out. Also check out the "drag", "platformer", "doublejump" demos with their own custom components.

Check out the component demo.