function validate(){
    var username=document.getElementById('login-username').value;
    var passowrd=document.getElementById('login-password').value;

    if (username === "daksh" && passowrd === 'daksh'){
        alert('You have sucessfully logged in');
        window.location.replace("http://stackoverflow.com");
    } else{
        alert('Wrong username or password');
        return true;
    }
}

<div action="login.html" class="container">
 <form  method="POST" class="login-form">
    <h1 class="login-heading">LOGIN FORM</h1>
     <input type="text" placeholder="User Name" id="login-username">
     <br><br>
     <input type="password" placeholder="Password" id="login-password">
     <br><br><br>
     <input type="submit" value="Login" id="login-submit" onclick="validate()">
 </form>
</div>