Why does push() on $router work?

Question

Vue.js

Why does this.$router have a push() method when it's not an array?

This code will output to the console the object we are pushing to when we write this.$router.push('/')

mounted() {
    console.log('this.$router', this.$router);
  },

Answer 1

This is an object.
And the push method is in its prototype __proto__

Answer 2

let a = {push(el) {console.log(el)}}
a.push(1)

also works and aalso not an array.