How to get props value to be used in emits array

I got a console error when I tried to list custom event in the component's emits option like this:

PARENT

<Btn
   event-name="toggleSideMenu"
   @toggle-side-menu="toggleHandler">
        toggle
 </Btn>

CHILD

<template>
   <button @click="handleClick">
      <slot></slot>
   </button>
</template>

export default {
   props: {
      eventName: {
         type: String,
         default: ''
      }
   },
   emits: [this.eventName], // Uncaught TypeError: Cannot read property 'eventName' of undefined
   methods: {
      handleClick() {
          this.$emit(this.eventName)
      }
   }
}

How is the correct way to get this thing to work?