Upgrade TS "target" to es2017 for ES module build

[ajhyndman]

It's not clear if this is an improvement or not.

The main difference here is that this allows us to output async/await keywords natively. Without this change, the code in "lib/" will contain a generated TS helper that polyfills async/await functionality.

Before

var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
    function adopt(value) { return value instanceof P ? value : new P(function (resolve) { resolve(value); }); }
    return new (P || (P = Promise))(function (resolve, reject) {
        function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
        function rejected(value) { try { step(generator["throw"](value)); } catch (e) { reject(e); } }
        function step(result) { result.done ? resolve(result.value) : adopt(result.value).then(fulfilled, rejected); }
        step((generator = generator.apply(thisArg, _arguments || [])).next());
    });
};
import { InViewportMutationObserver } from './inViewportMutationObserver';
import { waitForPageLoad } from './util';
import { requestAllIdleCallback } from './requestAllIdleCallback';
import { InViewportImageObserver } from './inViewportImageObserver';
import { Logger } from './util/logger';
/**
 * TODO: Document
 */
class VisuallyCompleteCalculator {
    constructor() {
        this.debug = false;
        this.idleTimeout = 200;
        // measurement state
        this.lastMutationTimestamp = 0;
        this.lastImageLoadTimestamp = 0;
        this.subscribers = new Set();
        this.navigationCount = 0;
        /** subscribe to Visually Complete metrics */
        this.getTTVC = (subscriber) => {
            // register subscriber callback
            this.subscribers.add(subscriber);
            // return an unsubscribe function
            return () => this.subscribers.delete(subscriber);
        };
        if (!VisuallyCompleteCalculator.isSupportedEnvironment()) {
            throw new Error('VisuallyCompleteCalculator: This browser/runtime is not supported.');
        }
        this.inViewportMutationObserver = new InViewportMutationObserver((mutation) => (this.lastMutationTimestamp = Math.max(this.lastMutationTimestamp, mutation.timestamp)));
        this.inViewportImageObserver = new InViewportImageObserver((timestamp) => (this.lastImageLoadTimestamp = Math.max(this.lastImageLoadTimestamp, timestamp)));
    }
    /**
     * Determine whether the calculator should run in the current environment
     */
    static isSupportedEnvironment() {
        var _a;
        return (window !== undefined &&
            'MutationObserver' in window &&
            'IntersectionObserver' in window &&
            typeof document.querySelectorAll === 'function' &&
            ((_a = window.performance) === null || _a === void 0 ? void 0 : _a.timing));
    }
    /** begin measuring a new navigation */
    start(start = 0) {
        return __awaiter(this, void 0, void 0, function* () {
            const navigationIndex = (this.navigationCount += 1);
            Logger.info('VisuallyCompleteCalculator.start()');
            // setup
            let shouldCancel = false;
            const cancel = () => (shouldCancel = true);
            this.inViewportImageObserver.observe();
            this.inViewportMutationObserver.observe(document.documentElement);
            window.addEventListener('pagehide', cancel);
            window.addEventListener('visibilitychange', cancel);
            window.addEventListener('locationchange', cancel);
            // attach user interaction listeners next tick (we don't want to pick up the SPA navigation click)
            window.setTimeout(() => {
                window.addEventListener('click', cancel);
                window.addEventListener('keydown', cancel);
            }, 0);
            // wait for page to be definitely DONE
            // - wait for window.on("load")
            yield waitForPageLoad();
            // - wait for simultaneous network and CPU idle
            const didNetworkTimeOut = yield new Promise(requestAllIdleCallback);
            if (!shouldCancel) {
                // identify timestamp of last visible change
                const end = Math.max(this.lastImageLoadTimestamp, this.lastMutationTimestamp);
                // report result to subscribers
                this.next({
                    start,
                    end,
                    duration: end - start,
                    detail: { didNetworkTimeOut },
                });
            }
            // cleanup
            window.removeEventListener('pagehide', cancel);
            window.removeEventListener('visibilitychange', cancel);
            window.removeEventListener('locationchange', cancel);
            window.removeEventListener('click', cancel);
            window.removeEventListener('keydown', cancel);
            // only disconnect observers if this is the most recent navigation
            if (navigationIndex === this.navigationCount) {
                this.inViewportImageObserver.disconnect();
                this.inViewportMutationObserver.disconnect();
            }
        });
    }
    next(measurement) {
        Logger.debug('VisuallyCompleteCalculator.next()', '::', 'lastImageLoadTimestamp =', this.lastImageLoadTimestamp, 'lastMutationTimestamp =', this.lastMutationTimestamp);
        Logger.info('TTVC:', measurement);
        this.subscribers.forEach((subscriber) => subscriber(measurement));
    }
}
// export calculator singleton
let calculator;
export const getVisuallyCompleteCalculator = () => {
    if (!calculator) {
        calculator = new VisuallyCompleteCalculator();
    }
    return calculator;
};

After

import { InViewportMutationObserver } from './inViewportMutationObserver';
import { waitForPageLoad } from './util';
import { requestAllIdleCallback } from './requestAllIdleCallback';
import { InViewportImageObserver } from './inViewportImageObserver';
import { Logger } from './util/logger';
/**
 * TODO: Document
 */
class VisuallyCompleteCalculator {
    constructor() {
        this.debug = false;
        this.idleTimeout = 200;
        // measurement state
        this.lastMutationTimestamp = 0;
        this.lastImageLoadTimestamp = 0;
        this.subscribers = new Set();
        this.navigationCount = 0;
        /** subscribe to Visually Complete metrics */
        this.getTTVC = (subscriber) => {
            // register subscriber callback
            this.subscribers.add(subscriber);
            // return an unsubscribe function
            return () => this.subscribers.delete(subscriber);
        };
        if (!VisuallyCompleteCalculator.isSupportedEnvironment()) {
            throw new Error('VisuallyCompleteCalculator: This browser/runtime is not supported.');
        }
        this.inViewportMutationObserver = new InViewportMutationObserver((mutation) => (this.lastMutationTimestamp = Math.max(this.lastMutationTimestamp, mutation.timestamp)));
        this.inViewportImageObserver = new InViewportImageObserver((timestamp) => (this.lastImageLoadTimestamp = Math.max(this.lastImageLoadTimestamp, timestamp)));
    }
    /**
     * Determine whether the calculator should run in the current environment
     */
    static isSupportedEnvironment() {
        var _a;
        return (window !== undefined &&
            'MutationObserver' in window &&
            'IntersectionObserver' in window &&
            typeof document.querySelectorAll === 'function' &&
            ((_a = window.performance) === null || _a === void 0 ? void 0 : _a.timing));
    }
    /** begin measuring a new navigation */
    async start(start = 0) {
        const navigationIndex = (this.navigationCount += 1);
        Logger.info('VisuallyCompleteCalculator.start()');
        // setup
        let shouldCancel = false;
        const cancel = () => (shouldCancel = true);
        this.inViewportImageObserver.observe();
        this.inViewportMutationObserver.observe(document.documentElement);
        window.addEventListener('pagehide', cancel);
        window.addEventListener('visibilitychange', cancel);
        window.addEventListener('locationchange', cancel);
        // attach user interaction listeners next tick (we don't want to pick up the SPA navigation click)
        window.setTimeout(() => {
            window.addEventListener('click', cancel);
            window.addEventListener('keydown', cancel);
        }, 0);
        // wait for page to be definitely DONE
        // - wait for window.on("load")
        await waitForPageLoad();
        // - wait for simultaneous network and CPU idle
        const didNetworkTimeOut = await new Promise(requestAllIdleCallback);
        if (!shouldCancel) {
            // identify timestamp of last visible change
            const end = Math.max(this.lastImageLoadTimestamp, this.lastMutationTimestamp);
            // report result to subscribers
            this.next({
                start,
                end,
                duration: end - start,
                detail: { didNetworkTimeOut },
            });
        }
        // cleanup
        window.removeEventListener('pagehide', cancel);
        window.removeEventListener('visibilitychange', cancel);
        window.removeEventListener('locationchange', cancel);
        window.removeEventListener('click', cancel);
        window.removeEventListener('keydown', cancel);
        // only disconnect observers if this is the most recent navigation
        if (navigationIndex === this.navigationCount) {
            this.inViewportImageObserver.disconnect();
            this.inViewportMutationObserver.disconnect();
        }
    }
    next(measurement) {
        Logger.debug('VisuallyCompleteCalculator.next()', '::', 'lastImageLoadTimestamp =', this.lastImageLoadTimestamp, 'lastMutationTimestamp =', this.lastMutationTimestamp);
        Logger.info('TTVC:', measurement);
        this.subscribers.forEach((subscriber) => subscriber(measurement));
    }
}
// export calculator singleton
let calculator;
export const getVisuallyCompleteCalculator = () => {
    if (!calculator) {
        calculator = new VisuallyCompleteCalculator();
    }
    return calculator;
};

[umairnadeem]

LGTM