@woosh/meep-engine/src/engine/intelligence/behavior/Behavior.js

Pure JavaScript game engine. Fully featured and production ready.

import Signal from "../../../core/events/signal/Signal.js";
import { BehaviorStatus } from "./BehaviorStatus.js";

/**
 * Base class of behavior tree implementation
 * @see "The Behavior Tree Starter Kit" by Alex J. Champandard and Philip Dunstan
 * @see https://en.wikipedia.org/wiki/Behavior_tree_(artificial_intelligence,_robotics_and_control)
 * @template CTX
 * @author Alex Goldring
 * @copyright Company Named Limited (c) 2025
 */
export class Behavior {

    /**
     * Any internal state used by the behavior
     * This provides a way to interact with the outside as well as to pass data between themselves
     * @type {CTX|null}
     */
    context = null;

    /**
     * Dispatched after initialization is complete
     * @readonly
     * @type {Signal<this,CTX>}
     */
    onInitialized = new Signal();

    /**
     * Dispatched after finalization is complete
     * @readonly
     * @type {Signal<this>}
     */
    onFinalized = new Signal();

    /**
     * Main update function. Every behavior executes some logic, some behaviors are long-running and some are instantaneous
     * @param {number} timeDelta time step in seconds
     * @returns {BehaviorStatus} signals status of the behavior, "success" or "failure" are used to signal completion of the behavior
     */
    tick(timeDelta) {
        throw new Error('Abstract method, needs to be overridden');
    }

    /**
     * Called before behavior gets executed via {@link #tick} for the first time
     * Used to prepare the behavior for execution
     * You can think of it as "start"
     * @param {CTX} [context]
     */
    initialize(context) {
        this.context = context;
        this.onInitialized.send2(this, context);
    }

    /**
     * Called when behavior is finished, or interrupted
     * Used to clean up any resources
     * You can think of it as "stop"
     */
    finalize() {
        // extend in subclasses as necessary
        this.onFinalized.send1(this);
    }
}

/**
 * Useful for type checking
 * @readonly
 * @type {boolean}
 */
Behavior.prototype.isBehavior = true;

/**
 * Useful for type checking
 * @readonly
 * @type {string}
 */
Behavior.typeName = "Behavior";