zenscroll.js

/**
 * Zenscroll 4.0.2
 * https://github.com/zengabor/zenscroll/
 *
 * Copyright 2015–2018 Gabor Lenard
 *
 * This is free and unencumbered software released into the public domain.
 * 
 * Anyone is free to copy, modify, publish, use, compile, sell, or
 * distribute this software, either in source code form or as a compiled
 * binary, for any purpose, commercial or non-commercial, and by any
 * means.
 * 
 * In jurisdictions that recognize copyright laws, the author or authors
 * of this software dedicate any and all copyright interest in the
 * software to the public domain. We make this dedication for the benefit
 * of the public at large and to the detriment of our heirs and
 * successors. We intend this dedication to be an overt act of
 * relinquishment in perpetuity of all present and future rights to this
 * software under copyright law.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 * 
 * For more information, please refer to <http://unlicense.org>
 * 
 */

/*jshint devel:true, asi:true */

/*global define, module */


(function (root, factory) {
	if (typeof define === "function" && define.amd) {
		define([], factory())
	} else if (typeof module === "object" && module.exports) {
		module.exports = factory()
	} else {
		(function install() {
			// To make sure Zenscroll can be referenced from the header, before `body` is available
			if (document && document.body) {
				root.zenscroll = factory()
			} else {
				// retry 9ms later
				setTimeout(install, 9)
			}
		})()
	}
}(this, function () {
	"use strict"


	// Detect if the browser already supports native smooth scrolling (e.g., Firefox 36+ and Chrome 49+) and it is enabled:
	var isNativeSmoothScrollEnabledOn = function (elem) {
		return elem && "getComputedStyle" in window &&
			window.getComputedStyle(elem)["scroll-behavior"] === "smooth"
	}


	// Exit if it’s not a browser environment:
	if (typeof window === "undefined" || !("document" in window)) {
		return {}
	}


	var makeScroller = function (container, defaultDuration, edgeOffset) {

		// Use defaults if not provided
		defaultDuration = defaultDuration || 999 //ms
		if (!edgeOffset && edgeOffset !== 0) {
			// When scrolling, this amount of distance is kept from the edges of the container:
			edgeOffset = 9 //px
		}

		// Handling the life-cycle of the scroller
		var scrollTimeoutId
		var setScrollTimeoutId = function (newValue) {
			scrollTimeoutId = newValue
		}

		/**
		 * Stop the current smooth scroll operation immediately
		 */
		var stopScroll = function () {
			clearTimeout(scrollTimeoutId)
			setScrollTimeoutId(0)
		}

		var getTopWithEdgeOffset = function (elem) {
			return Math.max(0, container.getTopOf(elem) - edgeOffset)
		}

		/**
		 * Scrolls to a specific vertical position in the document.
		 *
		 * @param {targetY} The vertical position within the document.
		 * @param {duration} Optionally the duration of the scroll operation.
		 *        If not provided the default duration is used.
		 * @param {onDone} An optional callback function to be invoked once the scroll finished.
		 */
		var scrollToY = function (targetY, duration, onDone) {
			stopScroll()
			if (duration === 0 || (duration && duration < 0) || isNativeSmoothScrollEnabledOn(container.body)) {
				container.toY(targetY)
				if (onDone) {
					onDone()
				}
			} else {
				var startY = container.getY()
				var distance = Math.max(0, targetY) - startY
				var startTime = new Date().getTime()
				duration = duration || Math.min(Math.abs(distance), defaultDuration);
				(function loopScroll() {
					setScrollTimeoutId(setTimeout(function () {
						// Calculate percentage:
						var p = Math.min(1, (new Date().getTime() - startTime) / duration)
						// Calculate the absolute vertical position:
						var y = Math.max(0, Math.floor(startY + distance*(p < 0.5 ? 2*p*p : p*(4 - p*2)-1)))
						container.toY(y)
						if (p < 1 && (container.getHeight() + y) < container.body.scrollHeight) {
							loopScroll()
						} else {
							setTimeout(stopScroll, 99) // with cooldown time
							if (onDone) {
								onDone()
							}
						}
					}, 9))
				})()
			}
		}

		/**
		 * Scrolls to the top of a specific element.
		 *
		 * @param {elem} The element to scroll to.
		 * @param {duration} Optionally the duration of the scroll operation.
		 * @param {onDone} An optional callback function to be invoked once the scroll finished.
		 */
		var scrollToElem = function (elem, duration, onDone) {
			scrollToY(getTopWithEdgeOffset(elem), duration, onDone)
		}

		/**
		 * Scrolls an element into view if necessary.
		 *
		 * @param {elem} The element.
		 * @param {duration} Optionally the duration of the scroll operation.
		 * @param {onDone} An optional callback function to be invoked once the scroll finished.
		 */
		var scrollIntoView = function (elem, duration, onDone) {
			var elemHeight = elem.getBoundingClientRect().height
			var elemBottom = container.getTopOf(elem) + elemHeight
			var containerHeight = container.getHeight()
			var y = container.getY()
			var containerBottom = y + containerHeight
			if (getTopWithEdgeOffset(elem) < y || (elemHeight + edgeOffset) > containerHeight) {
				// Element is clipped at top or is higher than screen.
				scrollToElem(elem, duration, onDone)
			} else if ((elemBottom + edgeOffset) > containerBottom) {
				// Element is clipped at the bottom.
				scrollToY(elemBottom - containerHeight + edgeOffset, duration, onDone)
			} else if (onDone) {
				onDone()
			}
		}

		/**
		 * Scrolls to the center of an element.
		 *
		 * @param {elem} The element.
		 * @param {duration} Optionally the duration of the scroll operation.
		 * @param {offset} Optionally the offset of the top of the element from the center of the screen.
		 *        A value of 0 is ignored.
		 * @param {onDone} An optional callback function to be invoked once the scroll finished.
		 */
		var scrollToCenterOf = function (elem, duration, offset, onDone) {
			scrollToY(Math.max(0, container.getTopOf(elem) - container.getHeight()/2 + (offset || elem.getBoundingClientRect().height/2)), duration, onDone)
		}

		/**
		 * Changes default settings for this scroller.
		 *
		 * @param {newDefaultDuration} Optionally a new value for default duration, used for each scroll method by default.
		 *        Ignored if null or undefined.
		 * @param {newEdgeOffset} Optionally a new value for the edge offset, used by each scroll method by default. Ignored if null or undefined.
		 * @returns An object with the current values.
		 */
		var setup = function (newDefaultDuration, newEdgeOffset) {
			if (newDefaultDuration === 0 || newDefaultDuration) {
				defaultDuration = newDefaultDuration
			}
			if (newEdgeOffset === 0 || newEdgeOffset) {
				edgeOffset = newEdgeOffset
			}
			return {
				defaultDuration: defaultDuration,
				edgeOffset: edgeOffset
			}
		}

		return {
			setup: setup,
			to: scrollToElem,
			toY: scrollToY,
			intoView: scrollIntoView,
			center: scrollToCenterOf,
			stop: stopScroll,
			moving: function () { return !!scrollTimeoutId },
			getY: container.getY,
			getTopOf: container.getTopOf
		}

	}


	var docElem = document.documentElement
	var getDocY = function () { return window.scrollY || docElem.scrollTop }

	// Create a scroller for the document:
	var zenscroll = makeScroller({
		body: document.scrollingElement || document.body,
		toY: function (y) { window.scrollTo(0, y) },
		getY: getDocY,
		getHeight: function () { return window.innerHeight || docElem.clientHeight },
		getTopOf: function (elem) { return elem.getBoundingClientRect().top + getDocY() - docElem.offsetTop }
	})


	/**
	 * Creates a scroller from the provided container element (e.g., a DIV)
	 *
	 * @param {scrollContainer} The vertical position within the document.
	 * @param {defaultDuration} Optionally a value for default duration, used for each scroll method by default.
	 *        Ignored if 0 or null or undefined.
	 * @param {edgeOffset} Optionally a value for the edge offset, used by each scroll method by default. 
	 *        Ignored if null or undefined.
	 * @returns A scroller object, similar to `zenscroll` but controlling the provided element.
	 */
	zenscroll.createScroller = function (scrollContainer, defaultDuration, edgeOffset) {
		return makeScroller({
			body: scrollContainer,
			toY: function (y) { scrollContainer.scrollTop = y },
			getY: function () { return scrollContainer.scrollTop },
			getHeight: function () { return Math.min(scrollContainer.clientHeight, window.innerHeight || docElem.clientHeight) },
			getTopOf: function (elem) { return elem.offsetTop }
		}, defaultDuration, edgeOffset)
	}


	// Automatic link-smoothing on achors
	// Exclude IE8- or when native is enabled or Zenscroll auto- is disabled
	if ("addEventListener" in window && !window.noZensmooth && !isNativeSmoothScrollEnabledOn(document.body)) {

		var isHistorySupported = "history" in window && "pushState" in history
		var isScrollRestorationSupported = isHistorySupported && "scrollRestoration" in history

		// On first load & refresh make sure the browser restores the position first
		if (isScrollRestorationSupported) {
			history.scrollRestoration = "auto"
		}

		window.addEventListener("load", function () {

			if (isScrollRestorationSupported) {
				// Set it to manual
				setTimeout(function () { history.scrollRestoration = "manual" }, 9)
				window.addEventListener("popstate", function (event) {
					if (event.state && "zenscrollY" in event.state) {
						zenscroll.toY(event.state.zenscrollY)
					}
				}, false)
			}

			// Add edge offset on first load if necessary
			// This may not work on IE (or older computer?) as it requires more timeout, around 100 ms
			if (window.location.hash) {
				setTimeout(function () {
					// Adjustment is only needed if there is an edge offset:
					var edgeOffset = zenscroll.setup().edgeOffset
					if (edgeOffset) {
						var targetElem = document.getElementById(window.location.href.split("#")[1])
						if (targetElem) {
							var targetY = Math.max(0, zenscroll.getTopOf(targetElem) - edgeOffset)
							var diff = zenscroll.getY() - targetY
							// Only do the adjustment if the browser is very close to the element:
							if (0 <= diff && diff < 9 ) {
								window.scrollTo(0, targetY)
							}
						}
					}
				}, 9)
			}

		}, false)

		// Handling clicks on anchors
		var RE_noZensmooth = new RegExp("(^|\\s)noZensmooth(\\s|$)")
		window.addEventListener("click", function (event) {
			var anchor = event.target
			while (anchor && anchor.tagName !== "A") {
				anchor = anchor.parentNode
			}
			// Let the browser handle the click if it wasn't with the primary button, or with some modifier keys:
			if (!anchor || event.which !== 1 || event.shiftKey || event.metaKey || event.ctrlKey || event.altKey) {
				return
			}
			// Save the current scrolling position so it can be used for scroll restoration:
			if (isScrollRestorationSupported) {
				var historyState = history.state && typeof history.state === "object" ? history.state : {}
				historyState.zenscrollY = zenscroll.getY()
				try {
					history.replaceState(historyState, "")
				} catch (e) {
					// Avoid the Chrome Security exception on file protocol, e.g., file://index.html
				}
			}
			// Find the referenced ID:
			var href = anchor.getAttribute("href") || ""
			if (href.indexOf("#") === 0 && !RE_noZensmooth.test(anchor.className)) {
				var targetY = 0
				var targetElem = document.getElementById(href.substring(1))
				if (href !== "#") {
					if (!targetElem) {
						// Let the browser handle the click if the target ID is not found.
						return
					}
					targetY = zenscroll.getTopOf(targetElem)
				}
				event.preventDefault()
				// By default trigger the browser's `hashchange` event...
				var onDone = function () { window.location = href }
				// ...unless there is an edge offset specified
				var edgeOffset = zenscroll.setup().edgeOffset
				if (edgeOffset) {
					targetY = Math.max(0, targetY - edgeOffset)
					if (isHistorySupported) {
						onDone = function () { history.pushState({}, "", href) }
					}
				}
				zenscroll.toY(targetY, null, onDone)
			}
		}, false)

	}


	return zenscroll


}));