An Elm Library for scrolling through a page and handling events. Meant to be used alongside StartApp.
$ elm package install abrykajlo/elm-scroll
$ git clone https://github.com/abrykajlo/elm-scroll
$ cd elm-scroll/examples
$ make elm
Open index.html in your browser.
First of all, the module is relying on the window.onscroll event, thus a port is needed:
<!DOCTYPE html>
<html>
<head>
<title>Adam Brykajlo</title>
<link rel="stylesheet" type="text/css" href="css/main.css">
<script type="text/javascript" src="js/main.js"></script>
</head>
<body>
<div id="main"></div>
<script>
var scroll = window.pageYOffset || document.body.scrollTop;
var mountNode = document.getElementById('main');
var myApp = Elm.Main.embed(mountNode);
window.onscroll = function() {
var newScroll = window.pageYOffset || document.body.scrollTop;
myApp.ports.scroll.send([scroll, newScroll]);
scroll = newScroll;
};
</script>
</body>
</html>Create a separate file for the ports:
-- Ports.elm
port module Ports exposing (..)
import Scroll exposing (Move)
port scroll : (Move -> msg) -> Sub msgIn your main file:
-- app definition
main =
App.program
{ init = init
, subscriptions = subscriptions
, update = update
, view = view
}Need to define at least two type of actions, one for the incoming port's messages and one for the animation frame:
type Action
= Header Move -- the message emitted by the input port
-- brings a tuple with previous and current scroll values
| Shrink -- message to be sent when scrollTop < 400px
| Grow -- message to be sent when scrollTop > 400px
| Animate Animation.Msg -- animation's tickFor the port to be handled, a new subscriptions has to be created:
subscriptions : Model -> Sub Action
subscriptions model =
Sub.batch
[ scroll Header
, Animation.subscription Animate [ model.style ]
]Finally, we need to handle properly all the messages:
update action model =
case action of
Grow ->
-- scrolling down, under 400px
-- ...
(model, Cmd.none)
Shrink ->
-- scrolling up, over 400px
-- ...
(model, Cmd.none)
Animate animMsg ->
-- here you can apply new styles, to be animated
--- ...
(model, Cmd.none)
Header move ->
Scroll.handle
[ update Grow -- when scrollTop > 400px, send Grow message
|> Scroll.onCrossDown 400
, update Shrink -- when scrollTop < 400px, send Shrink message
|> Scroll.onCrossUp 400
]
move modelEnjoy!