57 lines
1.8 KiB
Plaintext
57 lines
1.8 KiB
Plaintext
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class Follower
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(el) ->
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@follower = el
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@last-scroll-top = window.scroll-y
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@initial-follower-top = @follower.get-bounding-client-rect!.top
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@page-top = 48
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follow: ->
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window-height = window.inner-height
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follower-height = @follower.offset-height
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scroll-top = window.scroll-y
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scroll-bottom = scroll-top + window-height
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follower-top = @follower.get-bounding-client-rect!.top + scroll-top
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follower-bottom = follower-top + follower-height
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height-delta = Math.abs window-height - follower-height
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scroll-delta = @last-scroll-top - scroll-top
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is-scrolling-down = (scroll-top > @last-scroll-top)
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is-window-larger = (window-height > follower-height)
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console.log @initial-follower-top
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if (is-window-larger && scroll-top > @initial-follower-top) || (!is-window-larger && scroll-top > @initial-follower-top + height-delta)
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@follower.class-list.add \fixed
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else if !is-scrolling-down && scroll-top + @page-top <= @initial-follower-top
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@follower.class-list.remove \fixed
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@follower.style.top = 0
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return
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drag-bottom-down = (follower-bottom <= scroll-bottom && is-scrolling-down)
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drag-top-up = (follower-top >= scroll-top + @page-top && !is-scrolling-down)
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if drag-bottom-down
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console.log \down
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@follower.style.top = if is-window-larger then 0 else -height-delta + \px
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else if drag-top-up
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console.log \up
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@follower.style.top = @page-top + \px
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else if @follower.class-list.contains \fixed
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console.log \-
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current-top = parse-int @follower.style.top, 10
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min-top = -height-delta
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scrolled-top = current-top + scroll-delta
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is-page-at-bottom = (scroll-top + window-height >= document.body.offset-height)
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new-top = if is-page-at-bottom then min-top else scrolled-top
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@follower.style.top = new-top + \px
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@last-scroll-top = scroll-top
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module.exports = Follower
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