JSFiddle - React, Tailwind, and code Playground

HTML

<form>
<label name="username">Username</label>
                        <input id="username" type="text" minlength="6"
                            maxlength="20" pattern="[a-zA-Z0-9-]+" required>
                            
                                                    <label name="password">password</label>

                        <input id="password" type="password" minlength="6"
                            required>
                            <button onclick="store_data()" id="register" 
                            >Register</button>


</form>

JavaScript

let user_name = document.getElementById("username");
let user_paswrd = document.getElementById("password");


let store_data = () => {
  let input_username = localStorage.setItem("username", user_name.value);
  let input_password = localStorage.setItem("password", user_paswrd.value);

};