ClassWithoutConstructor.js

import React, { PureComponent } from "react";

import "./styles.css";

export default class Class extends PureComponent {
  state = {
    name: "Zagatti",
    count: 0
  };

  componentDidMount() {
    document.title = `${this.state.name}'s counter`;
  }

  componentDidUpdate(prevProps, prevState) {
    if (prevState.name !== this.state.name) {
      document.title = `${this.state.name}'s counter`;
    }
  }

  increment = () => {
    this.setState(state => {
      return { count: state.count + 1 };
    });
  };

  decrement = () => {
    this.setState(state => {
      return { count: state.count - 1 };
    });
  };

  updateName = e => {
    this.setState({ name: e.target.value });
  };

  render() {
    return (
      <div id="section">
        <div class="top">
          <label>Nome:</label>

          <input
            type="text"
            name="name"
            placeholder="Seu nome"
            value={this.state.name}
            onChange={this.updateName}
          />
        </div>

        <div class="buttons">
          <button onClick={this.decrement}>-</button>

          <span>{this.state.count}</span>

          <button onClick={this.increment}>+</button>
        </div>
      </div>
    );
  }
}