Add near-end threshold (#16)

Author: compulim

CHANGELOG.md

@@ -6,8 +6,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 ### Changed
-- `Composer`: fix [#13](https://github.com/compulim/react-scroll-to-bottom/pull/13), user scrolling in Firefox may have the scroll position locked occasionally, in PR [#12](https://github.com/compulim/react-scroll-to-bottom/pull/12)
-- `SpineTo`: fix [#10](https://github.com/compulim/react-scroll-to-bottom/pull/10) set stopping threshold from `0.5` to `1.5`, in PR [#14](https://github.com/compulim/react-scroll-to-bottom/pull/14)
+- `Composer`: fix [#13](https://github.com/compulim/react-scroll-to-bottom/issue/13), user scrolling in Firefox may have the scroll position locked occasionally, in PR [#12](https://github.com/compulim/react-scroll-to-bottom/pull/12)
+- `SpineTo`: fix [#10](https://github.com/compulim/react-scroll-to-bottom/issue/10), set stopping threshold from `0.5` to `1.5`, in PR [#14](https://github.com/compulim/react-scroll-to-bottom/pull/14)
+- `Composer`: fix [#15](https://github.com/compulim/react-scroll-to-bottom/issue/15), set near-end threshold from `0` to (less than) `1`, in PR [#16](https://github.com/compulim/react-scroll-to-bottom/pull/16)
 
 ## [1.3.0] - 2019-01-21
 ### Changed

packages/component/src/ScrollToBottom/Composer.js

@@ -1,4 +1,3 @@
-import memoize from 'memoize-one';
 import PropTypes from 'prop-types';
 import React from 'react';
 import updateIn from 'simple-update-in';
@@ -10,6 +9,7 @@ import SpineTo from '../SpineTo';
 import StateContext from './StateContext';
 
 const MIN_CHECK_INTERVAL = 17;       // 1 frame
+const NEAR_END_THRESHOLD = 1;
 const SCROLL_DECISION_DURATION = 34; // 2 frames
 
 function setImmediateInterval(fn, ms) {
@@ -19,8 +19,8 @@ function setImmediateInterval(fn, ms) {
 }
 
 function computeViewState({ stateContext: { mode }, target: { offsetHeight, scrollHeight, scrollTop } }) {
-  const atBottom = scrollHeight - scrollTop - offsetHeight <= 0;
-  const atTop = scrollTop <= 0;
+  const atBottom = scrollHeight - scrollTop - offsetHeight < NEAR_END_THRESHOLD;
+  const atTop = scrollTop < NEAR_END_THRESHOLD;
   const atEnd = mode === 'top' ? atTop : atBottom;
 
   return {