title: TypeError: Cannot read property 'signInWithPhoneNumber' of undefined
body: <p>result is defined but never used error occur but i can used see in code.</p>
  
  <p>and another occur in console 'Cannot read property 'signInWithPhoneNumber' of undefined'</p>
  
  <pre><code>sendOTP(){
       if(this.phoneNo.length!=10){
           alert('Invalid No.');
       }else{
           let countryCode="+91"
           let phoneNumber=countryCode+ this.phoneNo
           let appVerifier=this.appVerifier
  
           firebase.auth.signInWithPhoneNumber(phoneNumber, appVerifier)
           .then(function (confirmationResult){
               window.confirmationResult=confirmationResult;
               alert('SMS sent')
           }).catch(function(){
               alert('SMS not sent')
           })
       }
   },
  </code></pre>