You can get the key by using the function key() of any ref object

There are two ways to invoke push in Firebase's JavaScript SDK.

1. using push(newObject). This will generate a new push id and write the data at the location with that id.




2. using push(). This will generate a new push id and return a reference to the location with that id. This is a pure client-side
   operation.

Knowing #2, you can easily get a new push id client-side with:

var newKey = ref.push().key();

You can then use this key in your multi-location update.

https://stackoverflow.com/a/36774761/2305342

If you invoke the Firebase push() method without arguments it is a
pure client-side operation.

var newRef = ref.push(); // this does *not* call the server

You can then add the key() of the new ref to your item:

var newItem = {

    name: 'anauleau'

    id: newRef.key()

};

And write the item to the new location:

newRef.set(newItem);

https://stackoverflow.com/a/34437786/2305342

in your case :

writeUserData() {

  var myRef = firebase.database().ref().push();

  var key = myRef.key();



  var newData={

      id: key,

      Website_Name: this.web_name.value,

      Username: this.username.value,

      Password : this.password.value,

      website_link : this.web_link.value

   }



   myRef.push(newData);



}