My componentDidUpdate doesn't know the keyword this

Question

Hi I am trying to detect the auth state inside the class component. The auth state detection function comes from firebase doc.

componentDidUpdate() {
      firebase.auth().onAuthStateChanged(function(user) {
        if (user) {
          this.setState({
            displayDialog: true,
          })
        } else {
          this.setState({
            displayDialog: false,
          });
        }
      })
    }
  }

My problem is that the key word this is giving me this message & i don't know how to bind this to object like normal function,

"owner": "typescript",
    "message": "'this' implicitly has type 'any' because it does not have a type annotation.",
    "source": "ts",