Google Recaptcha V2验证过期后

Question

I used the google recaptcha v2 in long form. Before click the captcha validation handled by handleCorrectCaptcha method. If click the captcha checkbox then the captcha expired before the form submitting. Then when i click the submit button form becomes submitted without captcha. I don't know how to validate after captcha expired. Even i go through the https://support.google.com/recaptcha/?hl=en. I don't find the solution. Thanks in advance

My Html code is

<re-captcha (captchaResponse)="handleCorrectCaptcha($event)"  site_key="*****************************"></re-captcha>

My Angular2 Code is

handleCorrectCaptcha(captchaResponse: string) {
  this.captchaResponse=captchaResponse;
  this.appRef.tick();
}

Answer 1

HTML code is

<re-captcha (captchaResponse)="handleCorrectCaptcha($event)"  
site_key="*****************************" (captchaExpired)="handleExpired()">
</re-captcha>  

Angular2 Code is

handleCorrectCaptcha(captchaResponse: string) {
  this.captchaResponse=captchaResponse;
  this.appRef.tick();
}

handleExpired(){
  this.captchaResponse=null
}

I ask sorry for posting the simple question