HelloPlusModel.js

import HelloModel from 'https://agentscript.org/models/HelloModel.js'
import * as util from 'https://agentscript.org/src/utils.js'

// Here is a simple modification that allows setting the population dynamically.
// Note that speed & wiggle are already dynamic.
export default class HelloPlusModel extends HelloModel {
 population = 15 // override HelloModel
 minPopulation = 5
 maxPopulation = 25
 changeTick = 25 // set to null to avoid auto population changes

 // ======================

 // We can use Model's constructor, due to using Model's default World.
 // If you pass in world options, Model will use them
 constructor() {
 super() // use default world options.
 }

 step() {
 if (util.mod(this.ticks, this.changeTick) === 0) {
 // true when ticks = 0
 this.population = util.randomInt2(
 this.minPopulation,
 this.maxPopulation
 )
 console.log('new population', this.population)
 }
 this.checkPopulation()
 super.step()
 }
 checkPopulation() {
 // return if no change
 const delta = this.population - this.turtles.length
 if (delta === 0) return

 // add/remove turtles as needed
 if (delta < 0) {
 util.repeat(-delta, () => this.turtles.oneOf().die())
 } else {
 this.turtles.create(delta, t => t.moveTo(this.patches.oneOf()))
 }
 // make sure all turtles have at least one link
 this.turtles.ask(t => {
 if (t.links.length === 0) {
 this.links.create(t, this.turtles.otherOneOf(t))
 }
 })
 }
}