JS simple publish and subscribe class

The core idea

• Use a global variable to store the subscription function
• emit When triggered, traverse each variable of the corresponding array and execute
• off Delete the corresponding function from the array

// Some boundary treatments omitted here , Just to express the core implementation method in a minimalist way 

class Observe {
    
  cb = {
    }

  on(eventName, fn) {
    
    this.cb[eventName] = this.cb[eventName] || []
    this.cb[eventName].push(fn)
  }

  emit(eventName, data) {
    
    let arr = this.cb[eventName]
    if (arr) {
    
      arr.forEach((fn) => {
    
        fn(data)
      })
    }
  }

  off(eventName, fn) {
    
    let arr = this.cb[eventName]
    if (arr) {
    
      let newArr = fn ? arr.filter((e) => {
    
        return e !== fn
      }) : []
      this.cb[eventName] = newArr
    }
  }
}