How it works in known frameworks?

State is the essence of frameworks. It's what changes in applications.

Each state modification will make the concerned component to re-render its template with the according state new values.

State in Vuejs

const component = new View({
  data() {
    // initial state
    return { firstName: "Marvin" };
  },
  methods: {
    changeName() {
      // modifying the state
      this.firstName = "Thomas";
    }
  }
});

State in Angular

// initial state
this.firstName = "Marvin";

// modifying the state
handleClick() {
	this.firstName = "Thomas";
}

State in React

// initial state
this.state = { firstName: "Marvin" };

// modifying the state
this.setState({ firstName: "Thomas" });