How to clear the ionic storage before submitting the new data

I'm creating an ionic app with a webapp inside inappbrowser. I made a separate ionic login form that sends the credentials to the webapp's login form so that I can login in the webapp.

Here's the flow of my current code:

If the user has a saved credentials in the storage, open webapp and automatically login the user; else, stay on the login page.

But the problem is, if I clear the storage every time the user has a new login, it returns a null value.

Also, I'm not very sure if my code is a good practice, what's the other way for this?

userInput: string = "";
passInput: string = "";
userKey:string = 'username';
passKey:string = 'password';

constructor(
  private platform: Platform,
  private iab: InAppBrowser,
  private storage: Storage
) { this.init(); }

init() {
  let promiseList = [];

  Promise.all([
    this.storage.get(this.userKey).then((username) => {
      console.log('Retrieved username is', username);
      promiseList.push(username)
    }),
    this.storage.get(this.passKey).then((password) => {
      console.log('Retrieved password is', password);
      promiseList.push(password)
    })
  ]).then(() => {
    console.log('promiseList', promiseList)
    if (validated) { this.openWebApp(promiseList) }
    else { //remain in the login page }
  })
}

login() {
  // this.storage.clear()
  this.storage.set(this.userKey, this.userInput)
  this.storage.set(this.passKey, this.passInput)
  this.init();
}

openWebApp(credentials) {
  console.log('credentials', credentials, credentials[0], credentials[1])
  this.platform.ready().then(() => {
    const browser = this.iab.create('https://www.mywebapp.com/login', '_blank', {location:'no', footer:'no', zoom:'no', usewkwebview:'yes', toolbar:'no'});

    browser.on('loadstop').subscribe(event => {
    browser.show();

    browser.executeScript({
        code: `document.getElementById("usernameInput").value=${credentials[0]} document.getElementById("passwordInput").value=${credentials[1]} document.getElementById("submitBtn").click()`
    })
  });
});

Here's what I want to achieve:

If the user logs in again with a new credential, clear the old one and save the new one.

Ionic Storage functions usually return Promises... So you need to wait these Promises to resolve before doing other stuff... For example:

async login() {
  await this.storage.clear();
  await this.storage.set(this.userKey, this.userInput);
  await this.storage.set(this.passKey, this.passInput);
  this.init();
}