How to check a particle system exist or not

p5.js Libraries
1

Hi everyone here, I’m a newbie learning P5.js to do something interactive.
I’m facing a problem with I want to generate a particle system when receive a trigger from microphone. But when the trigger is on, the particle system will continuously generate.
I only want to generate one when triggered and if the trigger is off, then delete the particle system.

sketch.js

var systems
var mic

function setup() {
	c = createCanvas(1280,720);
	background(100);
	
	systems = []
	//for audio setting
	mic = new p5.AudioIn()
	mic.start()
}

function draw() {
	background(20, 10);

	var micLevel = mic.getLevel() * 1000
	console.log(micLevel)

	for (let i = 0; i < systems.length; i++) {
		systems[i].addBoid()
		systems[i].render()
	}
	
	// if micLevel over the threshold add a new BoidSystem
	if (micLevel > 40) {
		this.bs = new BoidSystem(createVector(679, 548))
		systems.push(bs)
	}
	if (micLevel < 40) {
		this.systems.splice(this.bs, 1)
	}
}
//can also add BoidSystem with Mouse
function mousePressed() {
	this.bs = new BoidSystem(createVector(mouseX, mouseY))
	systems.push(bs)
}

Boid class

var colors = "156064-00c49a-f8e16c-ffc2b4-fb8f67".split("-").map(a => "#" + a)
class Boid {
	constructor(position) {
		this.pos = position.copy() || createVector(width / 2, height / 2)
		this.target = createVector(0, 0)
		this.vel = createVector(0, 0)
		this.acc = p5.Vector.random2D().setMag(random(2, 8)) 
		this.r = 3
		this.color = random(colors)
		this.lifespan = 1600

	}
	run() {
		this.update()
		this.show()
	}
	update() {
		this.target = createVector(100, height / 2)
		this.pos.add(this.vel)
		this.vel = this.target.sub(this.pos).limit(3)
		this.acc.x+=(noise(this.pos.x)*0.1)
		this.acc.y+=(noise(this.pos.y)*0.1)
		this.vel.add(this.acc)
		this.acc.mult(0.94)
		this.lifespan -= 18

		//check border 
		if (this.pos.x > width || this.pos.x < 0) {
			this.vel.x *= -1
		}
		if (this.pos.y > width || this.pos.y < 0) {
			this.vel.y *= -1
		}

	}
	show() {
		// POINT boids
		push()
		translate(this.pos.x, this.pos.y)
		fill(this.color)
		noStroke()
		ellipse(0, 0, this.r)
		pop()
	}
	isDead() {
		return this.vel.mag() < 0.2
	}
}

BoidSystem class

class BoidSystem {
	constructor(position) {
		this.origin = position.copy()
		this.boids = []
	}
	addBoid() {
		this.boids.push(new Boid(this.origin))
	}
	render() {
		for (let i = this.boids.length - 1; i >= 0; i--) {
			let boid = this.boids[i]
			boid.run()
			if (boid.isDead()) {
				this.boids.splice(boid, 1)
			}
		}
	}
}