You can make use of html5's require property for simple form validation
<input type="firstname"
className="form-control"
id="firstname"
required
onChange={this.setFirstName}/>
Also one suggestion is that, I see you are calling different methods for every
fields. You can simple use
onChange={this.handleChange}
handleChange = (e) => {
const { value, id } = e.target;
this.setState({ [id]: e.target.value })
}
your state can be
state = {
lastname: '',
email: ''
} etc....
Your submit button will be
<button type="submit" className="btn btn-success" onSubmit= .
{this.handleSubmit}>Submit</button>
If you want to customize it, you can follow the link.
https://stackoverflow.com/questions/41296668/reactjs-form-input-validation