Vuex Store accessing state with 'this'

Question

I'm currently learning Vuex and reading this part of the official Vue documentation. I was wondering if there's a particular reason why we would access state with argument instead of just using this? I tested if things will work with this which it did.

Vue Example

const store = new Vuex.Store({
  state: {
    count: 1
  },
  mutations: {
    increment (state) {
      state.count++
    }
  }
})

My Example

const store = new Vuex.Store({
  state: {
    count: 1
  },
  mutations: {
    increment () {
      this.count++;
    }
  }
})

Answer 1

The Vuex store instance is not an ordinary object that has its own this, it could be seen as black box that offers some input/output for that it passes the state as parameter and then inside its logic (pattern) updates the state according to your mutation, for this available here:

 mutations: {
    increment () {
      this.count++;
    }
  }

it refers to the global window object.

According to @Spinx comments this refers to vuex instance in version 3 and later and i find that what @Matt said is a good note :

IMO this is a great example of why you should use the explicit parameter since you don't know how your function is bound __Matt