| 1 | /** |
| 2 | * Stop delayed or in-flight scrolling previously scheduled for an element. |
| 3 | * Virtualized containers call this before replacing their children so an old |
| 4 | * auto-scroll cannot override the restored viewport anchor. |
| 5 | */ |
| 6 | export function cancelPendingScroll(element) { |
| 7 | if (!element) return; |
| 8 | |
| 9 | const timeoutRaw = element.dataset?.scrollerTimeout; |
| 10 | const timeoutId = timeoutRaw == null ? null : Number(timeoutRaw); |
| 11 | if (Number.isFinite(timeoutId)) clearTimeout(timeoutId); |
| 12 | |
| 13 | if (element.dataset?.scrollingTo != null && element.scrollTo) { |
| 14 | element.scrollTo({ top: element.scrollTop, behavior: "instant" }); |
| 15 | } |
| 16 | |
| 17 | delete element.dataset.scrollerTimeout; |
| 18 | delete element.dataset.scrollerReapplySnapshot; |
| 19 | delete element.dataset.scrollingTo; |
| 20 | } |
| 21 | |
| 22 | export class Scroller { |
| 23 | constructor( |
| 24 | element, |
| 25 | { |
| 26 | smooth = false, |
| 27 | toleranceRem = 2, |
| 28 | reapplyDelayMs = 0, |
| 29 | reapplyToleranceRatio = 0, |
| 30 | applyStabilization = false, |
| 31 | } = {}, |
| 32 | ) { |
| 33 | this.element = element; |
| 34 | this.smooth = smooth; |
| 35 | this.reapplyDelayMs = reapplyDelayMs; |
| 36 | this.reapplyToleranceRatio = reapplyToleranceRatio; |
| 37 | this.tolerance = |
| 38 | toleranceRem * |
| 39 | parseFloat(getComputedStyle(document.documentElement).fontSize); |
| 40 | this.wasAtBottom = this.isAtBottom(); |
| 41 | this._scrollListener = null; |
| 42 | |
| 43 | this._resizeObserver = null; |
| 44 | this._lastClientHeight = null; |
| 45 | |
| 46 | if (applyStabilization) this._initScrollStabilization(); |
| 47 | } |
| 48 | |
| 49 | _initScrollStabilization() { |
| 50 | if (!this.element) return; |
| 51 | |
| 52 | const hasStabilizationFlag = |
| 53 | this.element?.dataset?.scrollStabilization != null; |
| 54 | if (hasStabilizationFlag) return; |
| 55 | |
| 56 | if (typeof ResizeObserver === "undefined") return; |
| 57 | |
| 58 | this._lastClientHeight = this.element.clientHeight; |
| 59 | this._resizeObserver = new ResizeObserver(() => { |
| 60 | const prevHeight = this._lastClientHeight; |
| 61 | const nextHeight = this.element.clientHeight; |
| 62 | |
| 63 | if (prevHeight == null) { |
| 64 | this._lastClientHeight = nextHeight; |
| 65 | return; |
| 66 | } |
| 67 | |
| 68 | if (nextHeight === prevHeight) return; |
| 69 | |
| 70 | const delta = nextHeight - prevHeight; |
| 71 | this._lastClientHeight = nextHeight; |
| 72 | |
| 73 | const scrollTop = this._getEffectiveScrollTop(); |
| 74 | const bottomDistanceBefore = |
| 75 | this.element.scrollHeight - scrollTop - prevHeight; |
| 76 | const wasAtBottom = bottomDistanceBefore <= this.tolerance; |
| 77 | this.wasAtBottom = wasAtBottom; |
| 78 | |
| 79 | if (wasAtBottom) { |
| 80 | this.scrollToBottom(); |
| 81 | return; |
| 82 | } |
| 83 | |
| 84 | if (delta !== 0) { |
| 85 | this._clearScrollingTo(); |
| 86 | this.element.scrollTop = Math.max(0, this.element.scrollTop - delta); |
| 87 | } |
| 88 | }); |
| 89 | |
| 90 | this._resizeObserver.observe(this.element); |
| 91 | |
| 92 | this.element.dataset.scrollStabilization = "1"; |
| 93 | } |
| 94 | |
| 95 | _getEffectiveScrollTop() { |
| 96 | const scrollingToRaw = this.element?.dataset?.scrollingTo; |
| 97 | const scrollingTo = scrollingToRaw == null ? null : Number(scrollingToRaw); |
| 98 | if (Number.isFinite(scrollingTo)) return scrollingTo; |
| 99 | return this.element.scrollTop; |
| 100 | } |
| 101 | |
| 102 | _setScrollingTo(target) { |
| 103 | this.element.dataset.scrollingTo = String(target); |
| 104 | |
| 105 | if (this._scrollListener) return; |
| 106 | |
| 107 | this._scrollListener = () => { |
| 108 | const current = this.element.scrollTop; |
| 109 | const activeTargetRaw = this.element?.dataset?.scrollingTo; |
| 110 | const activeTarget = activeTargetRaw == null ? null : Number(activeTargetRaw); |
| 111 | if (!Number.isFinite(activeTarget)) { |
| 112 | this._clearScrollingTo(); |
| 113 | return; |
| 114 | } |
| 115 | |
| 116 | if (current >= activeTarget - 1) this._clearScrollingTo(); |
| 117 | }; |
| 118 | |
| 119 | this.element.addEventListener("scroll", this._scrollListener, { |
| 120 | passive: true, |
| 121 | }); |
| 122 | } |
| 123 | |
| 124 | _clearScrollingTo() { |
| 125 | delete this.element.dataset.scrollingTo; |
| 126 | if (this._scrollListener) { |
| 127 | this.element.removeEventListener("scroll", this._scrollListener); |
| 128 | this._scrollListener = null; |
| 129 | } |
| 130 | } |
| 131 | |
| 132 | isAtBottom() { |
| 133 | const { scrollHeight, clientHeight } = this.element; |
| 134 | const scrollTop = this._getEffectiveScrollTop(); |
| 135 | return scrollHeight - scrollTop - clientHeight <= this.tolerance; |
| 136 | } |
| 137 | |
| 138 | _getBottomDistancePx() { |
| 139 | const { scrollHeight, clientHeight } = this.element; |
| 140 | const scrollTop = this._getEffectiveScrollTop(); |
| 141 | return scrollHeight - scrollTop - clientHeight; |
| 142 | } |
| 143 | |
| 144 | scrollToBottom() { |
| 145 | const target = Math.max( |
| 146 | 0, |
| 147 | this.element.scrollHeight - this.element.clientHeight, |
| 148 | ); |
| 149 | if (this.smooth) { |
| 150 | this._setScrollingTo(target); |
| 151 | this.element.scrollTo({ top: target, behavior: "smooth" }); |
| 152 | } else { |
| 153 | this._clearScrollingTo(); |
| 154 | this.element.scrollTop = target; |
| 155 | } |
| 156 | } |
| 157 | |
| 158 | _getReapplyTimeoutId() { |
| 159 | const raw = this.element?.dataset?.scrollerTimeout; |
| 160 | const parsed = raw == null ? null : Number(raw); |
| 161 | if (!Number.isFinite(parsed)) return null; |
| 162 | return parsed; |
| 163 | } |
| 164 | |
| 165 | _getReapplyScrollSnapshot() { |
| 166 | const raw = this.element?.dataset?.scrollerReapplySnapshot; |
| 167 | const parsed = raw == null ? null : Number(raw); |
| 168 | if (!Number.isFinite(parsed)) return null; |
| 169 | return parsed; |
| 170 | } |
| 171 | |
| 172 | _clearReapplyTimeout() { |
| 173 | const id = this._getReapplyTimeoutId(); |
| 174 | if (id != null) clearTimeout(id); |
| 175 | delete this.element.dataset.scrollerTimeout; |
| 176 | delete this.element.dataset.scrollerReapplySnapshot; |
| 177 | } |
| 178 | |
| 179 | _scheduleReapplyScrollToBottom() { |
| 180 | this._clearReapplyTimeout(); |
| 181 | |
| 182 | const snapshot = this._getEffectiveScrollTop(); |
| 183 | this.element.dataset.scrollerReapplySnapshot = String(snapshot); |
| 184 | |
| 185 | const id = setTimeout(() => { |
| 186 | delete this.element.dataset.scrollerTimeout; |
| 187 | |
| 188 | const expected = this._getReapplyScrollSnapshot(); |
| 189 | delete this.element.dataset.scrollerReapplySnapshot; |
| 190 | if (expected != null && this._getEffectiveScrollTop() !== expected) return; |
| 191 | |
| 192 | if (!this.wasAtBottom) return; |
| 193 | if (!this.isAtBottom()) return; |
| 194 | |
| 195 | this.scrollToBottom(); |
| 196 | }, this.reapplyDelayMs); |
| 197 | |
| 198 | this.element.dataset.scrollerTimeout = String(id); |
| 199 | } |
| 200 | |
| 201 | reApplyScroll(instant = false) { |
| 202 | this._clearReapplyTimeout(); |
| 203 | |
| 204 | if (!this.wasAtBottom) return; |
| 205 | |
| 206 | if (instant) { |
| 207 | this.scrollToBottom(); |
| 208 | return; |
| 209 | } |
| 210 | |
| 211 | if (!this.isAtBottom()) { |
| 212 | this.scrollToBottom(); |
| 213 | return; |
| 214 | } |
| 215 | |
| 216 | const ratio = this.reapplyToleranceRatio; |
| 217 | if (ratio <= 0) { |
| 218 | if (this.reapplyDelayMs > 0) this._scheduleReapplyScrollToBottom(); |
| 219 | else this.scrollToBottom(); |
| 220 | return; |
| 221 | } |
| 222 | |
| 223 | const dist = this._getBottomDistancePx(); |
| 224 | const tolerance = this.tolerance; |
| 225 | const clampedDist = Math.max(0, Math.min(dist, tolerance)); |
| 226 | const progress = tolerance > 0 ? 1 - clampedDist / tolerance : 1; |
| 227 | if (progress < ratio) return; |
| 228 | |
| 229 | if (this.reapplyDelayMs > 0) this._scheduleReapplyScrollToBottom(); |
| 230 | else this.scrollToBottom(); |
| 231 | } |
| 232 | } |