javascript - Firebase does multiple calls even with if/else statement JS -

i building app vue , firebase. new firebase , i've problems it. try store names + emails in database. want check first if email in database , if not, run function store name + email. if email stored in database output alert , cancel submit.

so check of email in database going quite well, output alert, , able retrieve data. problem lays when enter email not in database. when enter new email (and name) check database , return false right away call (i dont know why, that's problem guess) , return true, , alert of being there, @ same time. proceed function store data because output of first call (which false).

my js code:

checkform() {          let app = this;          if (this.name == '' || this.emailadress == '') {             alert('you have fill out form');         } else {              app.getfirebase();          } },  getfirebase() {          let app = this;          var ref = firebase.database().ref().child('/aanmeldingen/');         ref.on('value', function(snapshot) {              const array = [];              snapshot.foreach(function(childsnapshot) {               var checkemail = childsnapshot.val().email;               array.push(checkemail);             });              const res = array.includes(app.emailadress);             console.log(array);             console.log(res);                if(res) {                 alert('you have entered giveaway');               } else if (res == false) {                  app.store();                }         }); },  store() {                 this.step_two = false;                 this.active_two = false;                  this.active_three = true;                 this.step_three = true;                  let app = this;                  firebase.database().ref('/aanmeldingen/').push({                 username: app.name,                 email: app.emailadress,                 }); } 

screenshot of console (entered jane, not in database)

you should using once() instead of on(). on() leaves listener attached, when push data in store() listener fires again.