babylon.js + nengi.js entity example. Note: one can write the same thing in more of an ECS style (instead of regular oop) if desired by moving all of the methods off of PlayerCharacter and into systems

PlayerCharacter.js

import nengi from 'nengi'
import * as BABYLON from 'babylonjs'

class PlayerCharacter {
    constructor(scene) {
        this.name = 'anon'
        this.mesh = new BABYLON.Mesh('dummy', scene)
        this.mesh.entity = this // for collisions within babylon
        this.hitpoints = 100
        // velocity from own impulses
        this.velocity = new BABYLON.Vector3(0, 0, 0)
        // velocity from external impulses (explosions, pushes, etc)
        this.evelocity = new BABYLON.Vector3(0, 0, 0)
        this.jumpCooldown = new Cooldown(0.5)
        this.sprintCooloff = new Cooloff(0.33)
        this.scene = scene
    }

    get x() { return this.mesh.position.x }
    set x(value) { this.mesh.position.x = value }

    get y() { return this.mesh.position.y }
    set y(value) { this.mesh.position.y = value }

    get z() { return this.mesh.position.z }
    set z(value) { this.mesh.position.z = value }
  
    /* skipped rotationX, etc */

    dispose() {
        this.mesh.dispose()
    }
    
    processInput(command) {
       // movement logic goes  here
    }

    takeDamage(sourceClient, amount, fromPosition, fromId) {
      // ...
    }

    ressurect() {
        this.hitpoints = 100
        //... respawn
    }

    getForwardRay() {
        this.mesh.computeWorldMatrix(true)
        const f = BABYLON.Vector3.TransformCoordinates(BABYLON.Vector3.Forward(), this.mesh.getWorldMatrix())
        const d = f.subtract(this.mesh.position)
        const v = d.normalize()
        return new BABYLON.Ray(this.mesh.position, v, 999)
    }
}

PlayerCharacter.protocol = {
    x: { type: nengi.Float64, interp: true },
    y: { type: nengi.Float64, interp: true },
    z: { type: nengi.Float64, interp: true },
    rotationX: { type: nengi.RotationFloat32, interp: true },
    rotationY: { type: nengi.RotationFloat32, interp: true },
    rotationZ: { type: nengi.RotationFloat32, interp: true },
    name: nengi.String,
    hitpoints: { type: nengi.UInt8, interp: true },
}

/* because there are getters/setters for x, y, z, rotationX, etc
* recreating this entity on the client is as simply as:
* const player = new PlayerCharacter(scene)
* Object.assign(player, networkDataForPlayer)
* */

export default PlayerCharacter