js simple and crude publish and subscribe sample code

class Publish {
 constructor() {
  this.listMap = {};
 }
	// Subscribe on(key, fn) {
  this.listMap[key]
   ? this.listMap[key].push(fn)
   : this.listMap[key] = [fn];
   
		//Store the subscript of subscription fn const index = this.listMap[key].length - 1;
  
		// Return the unsubscribe function
  return () => this.clear(key, index);
 }
 
	// Cancel all subscriptions to this key off(key) {
  delete this.listMap[key];
 }
 
	// Cancel a subscription specified by key clear(key, index) {
  index === this.listMap[key].length - 1
   ? this.listMap[key].pop()
   : this.listMap[key][index] = null;
 }
 
	//Subscribe once and automatically unsubscribe after triggering once(key, fn) {
  this.on(key, (...rest) => {
   fn(...rest);
   this.off(key);
  });
 }

	// Publish key
 trigger(key, ...rest) {
 	if(key in this.listMap) {
	 	this.listMap[key].forEach(fn => {
	   fn(...rest);
	  });
 	}
 }
}

const ob = new Publish();

//Subscribe to sub1
const sub1 = ob.on('sub1', (a, b) => {
 console.log('sub1', a, b);
});

//Subscribe to sub1
const sub11 = ob.on('sub1', (a, b) => {
 console.log('sub11', a, b);
});

ob.trigger('sub1', 2, 3);

// Unsubscribe from sub1
sub1();

// Unsubscribe from sub11
sub11();

//Subscribe to sub3
ob.on('sub3', (a, b) => {
 console.log('sub3', a, b);
});

//Subscribe to sub3
ob.on('sub3', (a, b) => {
 console.log('sub33', a, b);
});

ob.trigger('sub3', 6, 7);

// Unsubscribe from all sub3
ob.off('sub3');

// Subscribe once and unsubscribe automatically ob.once('sub4', (a, b) => {
 console.log('sub4', a, b);
});

ob.trigger('sub4', 8, 9);