Programmatically set username/password in the login form in safari mobile and the values set are not being recognized by form submit

I am going to implement password saving/autofill in my react-native-webview. I implemented to save password when user first enter the username/password and then load that credential and assign the credential to that login form. The username and password are successfully written to the input elements.
The problem is that, when user submits the login form by clicking [Sign In] button, the login page recognizes the username and password elements are empty.
I hope anyone can teach me what should I do to solve this problem.

      var usernameEle = document.querySelector('[autocomplete="username"]');
      if(usernameEle) {

        usernameEle.setAttribute("value", "${ username }");
        usernameEle.value = "${ username }";

        setTimeout(() => {
          usernameEle.focus();
          usernameEle.blur();

          usernameEle.dispatchEvent(new KeyboardEvent("keydown", { key: "e" }));
          usernameEle.dispatchEvent(new Event("change", { bubbles: true }));
          usernameEle.dispatchEvent(new Event("change", { bubbles: true }));

        }, 100);
      }