seng-scroll-tracker/lib/ScrollTrackerPoint.js

Class that keeps track of the vertical scroll position of an element.

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
var tslib_1 = require("tslib");
var seng_event_1 = require("seng-event");
var Side_1 = require("./enum/Side");
var ScrollTrackerEvent_1 = require("./event/ScrollTrackerEvent");
/**
 * Instance created for every coordinate that a ScrollTracker tracks.
 */
var ScrollTrackerPoint = /** @class */ (function (_super) {
    tslib_1.__extends(ScrollTrackerPoint, _super);
    function ScrollTrackerPoint(scrollPosition, pointHeight, pointSide, pointTracker) {
        var _this = _super.call(this) || this;
        _this.scrollPosition = scrollPosition;
        _this.pointHeight = pointHeight;
        _this.pointSide = pointSide;
        _this.pointTracker = pointTracker;
        /**
         * Boolean indicating if the point is currently in view. Updated when checkInView() is called.
         */
        _this.isInView = false;
        /**
         * Boolean indicating if the point is currently within the bounds of the target element.
         * Updated when checkInView() is called.
         */
        _this.isInBounds = false;
        /**
         * Boolean indicating if the top of the viewport has been scrolled beyond this point
         */
        _this.hasScrolledBeyond = false;
        setTimeout(function () {
            if (_this.isDisposed()) {
                return;
            }
            _this.checkScrollBeyond();
            _this.isInView = _this.getInViewValue();
        }, 0);
        return _this;
    }
    Object.defineProperty(ScrollTrackerPoint.prototype, "position", {
        /**
         * @returns {number} The current position of the point in pixels. This is the distance from the
         * start or end of the target element depending on the 'side' parameter, measured horizontally or
         * vertically depending on the axis of this ScrollTracker instance.
         */
        get: function () {
            return this.scrollPosition;
        },
        /**
         * Change the position of this point. Executes checkInView to check if the point has entered or
         * leaved view.
         * @param position The position of this points in pixels. This is the distance from the start
         * or end of the target element depending on the 'side' parameter, measured horizontally or
         * vertically depending on the axis of this ScrollTracker instance.
         */
        set: function (position) {
            this.scrollPosition = position;
            this.checkInView();
        },
        enumerable: true,
        configurable: true
    });
    Object.defineProperty(ScrollTrackerPoint.prototype, "height", {
        /**
         * @returns {number} The current height of the point in pixels. This is the distance from the
         * start or end of the target element depending on the 'side' parameter, measured horizontally or
         * vertically depending on the axis of this ScrollTracker instance.
         */
        get: function () {
            return this.pointHeight;
        },
        /**
         * Change the height of this point. Executes checkInView to check if the point has entered or
         * leaved view.
         * @param height The height of this points in pixels. This is the distance from the start
         * or end of the target element depending on the 'side' parameter, measured horizontally or
         * vertically depending on the axis of this ScrollTracker instance.
         */
        set: function (height) {
            this.pointHeight = height;
            this.checkInView();
        },
        enumerable: true,
        configurable: true
    });
    Object.defineProperty(ScrollTrackerPoint.prototype, "side", {
        /**
         * @returns {Side} The side of from which the position of this point is measured.
         */
        get: function () {
            return this.pointSide;
        },
        enumerable: true,
        configurable: true
    });
    ScrollTrackerPoint.prototype.getInViewValue = function () {
        var viewEnd = this.pointTracker.viewEnd; // pageYOffset + windowHeight
        return viewEnd >= this.scrollPosition &&
            viewEnd <= this.scrollPosition + this.pointHeight + window.innerHeight;
    };
    ScrollTrackerPoint.prototype.checkScrollBeyond = function () {
        var positionFromStart = this.pointSide === Side_1.default.START ?
            this.scrollPosition : this.pointTracker.scrollSize - this.scrollPosition;
        if (!this.hasScrolledBeyond) {
            var hasScrolledBeyond = this.pointTracker.viewEnd >= positionFromStart;
            if (hasScrolledBeyond) {
                this.hasScrolledBeyond = true;
            }
        }
    };
    /**
     * Checks if this point is in view using it's position and the current scroll position saved on
     * the ScrollTracker. Updates the isInView property accordingly.
     * @return {boolean} True if this point is in view.
     */
    ScrollTrackerPoint.prototype.checkInView = function (scrollingBack) {
        if (scrollingBack === void 0) { scrollingBack = false; }
        var isInView = this.getInViewValue();
        this.isInBounds = this.scrollPosition >= 0 && this.scrollPosition <= this.pointTracker.viewEnd;
        var positionFromStart = this.pointSide === Side_1.default.START ?
            this.scrollPosition : this.pointTracker.scrollSize - this.scrollPosition;
        if (this.isInView !== isInView) {
            this.isInView = isInView;
            var eventType = isInView ?
                ScrollTrackerEvent_1.default.types.ENTER_VIEW : ScrollTrackerEvent_1.default.types.LEAVE_VIEW;
            var event_1 = new ScrollTrackerEvent_1.default(eventType, this, (isInView ? scrollingBack : !scrollingBack) ? Side_1.default.START : Side_1.default.END);
            this.dispatchEvent(event_1);
        }
        if (!this.hasScrolledBeyond && this.pointTracker.viewEnd >= positionFromStart && !isInView) {
            this.hasScrolledBeyond = true;
            this.dispatchEvent(new ScrollTrackerEvent_1.default(ScrollTrackerEvent_1.default.types.SCROLLED_BEYOND, this, Side_1.default.END));
        }
        return this.isInView;
    };
    /**
     * Disposes the ScrollTrackerPoint instance.
     */
    ScrollTrackerPoint.prototype.dispose = function () {
        this.pointTracker = null;
        _super.prototype.dispose.call(this);
    };
    return ScrollTrackerPoint;
}(seng_event_1.default));
exports.default = ScrollTrackerPoint;