app.get('/public.userinfo',(request, response) => {
    client.query('SELECT * FROM userinfo WHERE userin_id, username=$1 AND password=$2 '[request.body.username, request.body.password],
    result => response.send(result.row)
  )
  .catch(console.error);
});

$.ajax({
    url:`public.userinfo`,
    method:'GET',
    dataType: 'json',
    data: {username:this.username, password:this.password, win:this.win, loss:this.loss},
    success: function(result){
      console.log(result);

    },
    error:function(err){
      console.log(err);
    }



 });

<form class="login" method= "GET" action="/public.userinfo" id="login">
    <input type="text" name="username" id="username" class="username">
    <input type="password" name="password" id="password" class="password">
    <button value="submit" name="login" id="loginButton">Login</button>
    <span id="login_message"></span>
  </form>