title: How to highlight empty mandatory(*) input field with red border click on button in React?
body: <p>In below image screenshot I make fields mandatory so click on register button If any fields then that empty field I want to highlight with red border in React how it is possible ?
   (<a href="https://blueprintjs.com/docs/#core/components/text-inputs" rel="nofollow noreferrer">https://blueprintjs.com/docs/#core/components/text-inputs</a>) </p>
  
  <p><a href="https://i.stack.imgur.com/vtedM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/vtedM.png" alt="form"></a></p>
  
  <pre><code>constructor(props) {
      super(props);
      this.state = {
          firstName: '',
          lastName: '',
          email: '',
          password: '',
      };
      this.handleChange = this.handleChange.bind(this);
      this.registerForm = this.registerForm.bind(this);
  }
  
  handleChange(event) {
      this.setState({[event.target.name]: event.target.value});
  }
  
  registerForm(){
      if(this.state.firstName.trim() &amp;&amp; this.state.lastName.trim() &amp;&amp; 
         this.state.email &amp;&amp; this.state.password){
           console.log("registration successfully..!!"); 
      }else{
           console.log("all * marked fields mandatory");
      }
  }
  
  render() {
    return (
      &lt;div&gt;
        &lt;h2&gt;Fill Registration Details..!!&lt;/h2&gt;
          &lt;InputGroup placeholder="Enter First Name...*"            
            name="firstName" value={this.state.firstName} onChange={this.handleChange}/&gt;
  
          &lt;InputGroup placeholder="Enter Last Name...*" name="lastName" 
           value={this.state.lastName} onChange={this.handleChange}/&gt;
  
          &lt;InputGroup placeholder="Enter your email...*" name="email"
           value={this.state.email} onChange={this.handleChange}/&gt;
  
          &lt;InputGroup placeholder="Enter your password...*"name="password" 
           value={this.state.password} onChange={this.handleChange}/&gt;
  
          &lt;Button intent="Primary" onClick={this.registerForm}&gt;Register&lt;/Button&gt;
         &lt;/div&gt;
      )
    }
  </code></pre>