git ssb

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// FROM: https://raw.githubusercontent.com/dominictarr/pull-scroll/master/index.js
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var pull = require('pull-stream')
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var Pause = require('pull-pause')
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var isVisible = require('is-visible').isVisible
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var next = 'undefined' === typeof setImmediate ? setTimeout : setImmediate
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function isBottom (scroller, buffer) {
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  var rect = scroller.getBoundingClientRect()
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  var topmax = scroller.scrollTopMax || (scroller.scrollHeight - rect.height)
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  return scroller.scrollTop >=
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    + ((topmax) - (buffer || 0))
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}
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function isTop (scroller, buffer) {
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  return scroller.scrollTop <= (buffer || 0)
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}
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function isFilled(content) {
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  return (
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    !isVisible(content)
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    //check if the scroller is not visible.
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   // && content.getBoundingClientRect().height == 0
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    //and has children. if there are no children,
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    //it might be size zero because it hasn't started yet.
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//    &&
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    && content.children.length > 20
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    //&& !isVisible(scroller)
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  )
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}
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function isEnd(scroller, buffer, top) {
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  //if the element is display none, don't read anything into it.
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  return (top ? isTop : isBottom)(scroller, buffer)
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}
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function append(scroller, list, el, top, sticky) {
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  if(!el) return
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  var s = scroller.scrollHeight
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  if(top && list.firstChild)
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    list.insertBefore(el, list.firstChild)
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  else
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    list.appendChild(el)
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  //scroll down by the height of the thing added.
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  //if it added to the top (in non-sticky mode)
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  //or added it to the bottom (in sticky mode)
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  if(top !== sticky) {
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    var st = list.scrollTop, d = (scroller.scrollHeight - s) + 1
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    scroller.scrollTop = scroller.scrollTop + d
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  }
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}
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function overflow (el) {
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  return el.style.overflowY || el.style.overflow || (function () {
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    var style = getComputedStyle(el)
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    return style.overflowY || el.style.overflow
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  })()
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}
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var buffer = 1000
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module.exports = function Scroller(scroller, content, render, top, sticky, cb) {
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  //if second argument is a function,
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  //it means the scroller and content elements are the same.
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  if('function' === typeof content) {
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    cb = sticky
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    top = render
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    render = content
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    content = scroller
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  }
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  if(!cb) cb = function (err) { if(err) throw err }
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  var f = overflow(scroller)
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  if(!/auto|scroll/.test(f))
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    throw new Error('scroller.style.overflowY must be scroll or auto, was:' + f + '!')
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  scroller.addEventListener('scroll', scroll)
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  var pause = Pause(function () {}), queue = []
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  //apply some changes to the dom, but ensure that
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  //`element` is at the same place on screen afterwards.
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  function add () {
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    if(queue.length)
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      append(scroller, content, render(queue.shift()), top, sticky)
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  }
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  function scroll (ev) {
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    if (isEnd(scroller, buffer, top) || isFilled(content)) {
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      pause.resume()
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      add()
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    }
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  }
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  // pause.pause()
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  //
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  // //wait until the scroller has been added to the document
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  // next(function next () {
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  //   if(scroller.parentElement) pause.resume()
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  //   else                       setTimeout(next, 100)
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  // })
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  var stream = pull(
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    pause,
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    pull.drain(function (e) {
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      queue.push(e)
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      //we don't know the scroll bar positions if it's display none
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      //so we have to wait until it becomes visible again.
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      if(!isVisible(content)) {
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        if(content.children.length < 20) add()
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      }
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      else if(isEnd(scroller, buffer, top)) add()
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      if(queue.length > 10) pause.pause()
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    }, function (err) {
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      scroller.removeEventListener('scroll', scroll)
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      if(err) console.error(err)
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      cb ? cb(err) : console.error(err)
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    })
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  )
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  stream.visible = add
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  return stream
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}
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