User:Jdlrobson/scripts/backtotop.js

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Documentation for this user script can be added at User:Jdlrobson/scripts/backtotop. This user script seems to have an accompanying .css page at User:Jdlrobson/scripts/backtotop.css.

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mw.loader.load( '/w/index.php?title=User:Jdlrobson/scripts/backtotop.css&action=raw&ctype=text/css', 'text/css' ).then(function () {
	var backtotop,
		// eslint-disable-next-line no-restricted-properties
		M = mw.mobileFrontend,
		mobile = M.require( 'mobile.startup' ),
		View = mobile.View,
		features = mw.config.get( 'wgMinervaFeatures', {} ),
		browser = mobile.Browser.getSingleton(),
		eventBus = mobile.eventBusSingleton;

	/**
	 * Displays a little arrow at the bottom right of the viewport.
	 * @class BackToTopOverlay
	 * @extends View
	 * @param {Object} props
	 */
	function BackToTopOverlay( props ) {
		View.call( this,
			$.extend( {}, props, {
				className: 'backtotop',
				events: { click: 'onBackToTopClick' }
			} )
		);
	}

	OO.inheritClass( BackToTopOverlay, View );

	BackToTopOverlay.prototype.template = mw.template.get( 'skins.minerva.options', 'BackToTopOverlay.mustache' );

	/**
	 * Show the back to top element, if it's not visible already.
	 * @memberof BackToTopOverlay
	 * @instance
	 */
	BackToTopOverlay.prototype.show = function () {
		this.$el.css( 'visibility', 'visible' ).addClass( 'visible' );
	};

	/**
	 * Hide the back to top element, if it's visible.
	 * @memberof BackToTopOverlay
	 * @instance
	 */
	BackToTopOverlay.prototype.hide = function () {
		this.$el.removeClass( 'visible' );
	};

	/**
	 * Handles the click on the "Back to top" element and scrolls back
	 * to the top smoothly.
	 * @memberof BackToTopOverlay
	 * @instance
	 */
	BackToTopOverlay.prototype.onBackToTopClick = function () {
		// eslint-disable-next-line no-jquery/no-global-selector
		$( 'html, body' ).animate( { scrollTop: 0 }, 400 );
	};


	// check if browser user agent is iOS (T141598)
	if ( browser.isIos() || !features.backToTop ) {
		return;
	} else {
		backtotop = new BackToTopOverlay();
		// initialize the back to top element
		backtotop.appendTo( 'body' );

		eventBus.on( 'scroll', function () {
			if ( $( window ).height() - $( window ).scrollTop() <= 0 ) {
				backtotop.show();
			} else {
				backtotop.hide();
			}
		} );	
	}
});