timer.js

/*! timer.js v3.0.0
 * https://github.com/adamcik/media-progress-timer
 * Copyright (c) 2015-2016 Thomas Adamcik
 * Licensed under the Apache License, Version 2.0 */

(function (root, factory) {
    if (typeof define === 'function' && define.amd) {
        define([], factory);
    } else if (typeof module === 'object' && module.exports) {
        module.exports = factory();
    } else {
        root.ProgressTimer = factory();
    }
}(this, function () {
    'use strict';

    // Helper function to provide a reference time in milliseconds.
    var now = typeof window.performance !== 'undefined' &&
              typeof window.performance.now !== 'undefined' &&
              window.performance.now.bind(window.performance) || Date.now ||
              function() { return new Date().getTime(); };

    // Helper to warn library users about deprecated features etc.
    function warn(msg) {
        window.setTimeout(function() { throw msg; }, 0);
    }

    // Creates a new timer object, works with both 'new ProgressTimer(options)'
    // and just 'ProgressTimer(options). Optionally the timer can also be
    // called with only the callback instead of options.
    function ProgressTimer(options) {
        if (!(this instanceof ProgressTimer)) {
            return new ProgressTimer(options);
        } else if (typeof options === 'function') {
            options = {'callback': options};
        } else if (typeof options !== 'object') {
            throw '"ProgressTimer" must be called with a callback or options.';
        } else if (typeof options['callback'] !== 'function') {
            throw '"ProgressTimer" needs a callback to operate.';
        }

        this._userCallback = options['callback'];
        this._updateId = null;
        this._state = null;  // Gets initialized by the set() call.

        var frameDuration = 1000 / (options['fallbackTargetFrameRate'] || 30);
        // TODO: Remove this legacy code path at some point.
        if (options['updateRate'] && !options['fallbackTargetFrameRate']) {
            warn('"ProgressTimer" no longer supports the updateRate option.');
            frameDuration = Math.max(options['updateRate'], 1000 / 60);
        }

        var useFallback = (
            typeof window.requestAnimationFrame === 'undefined' ||
            typeof window.cancelAnimationFrame === 'undefined' ||
            options['disableRequestAnimationFrame'] || false);

        // Make sure this works in _update.
        var update = this._update.bind(this);

        if (useFallback) {
            this._schedule = function(timestamp) {
                var timeout = Math.max(timestamp + frameDuration - now(), 0);
                return window.setTimeout(update, Math.floor(timeout));
            };
            this._cancel = window.clearTimeout.bind(window);
        } else {
            this._schedule = window.requestAnimationFrame.bind(window, update);
            this._cancel = window.cancelAnimationFrame.bind(window);
        }

        this.reset(); // Reuse reset code to ensure we start in the same state.
    }

    // If called with one argument the previous duration is preserved. Note
    // that the position can be changed while the timer is running.
    ProgressTimer.prototype.set = function(position, duration) {
        if (arguments.length === 0) {
            throw '"ProgressTimer.set" requires the "position" arugment.';
        } else if (arguments.length === 1) {
            // Fallback to previous duration, whatever that was.
            duration = this._state.duration;
        } else {
            // Round down and make sure zero and null are treated as inf.
            duration = Math.floor(Math.max(
                duration === null ? Infinity : duration || Infinity, 0));
        }
        // Make sure '0 <= position <= duration' always holds.
        position = Math.floor(Math.min(Math.max(position || 0, 0), duration));

        this._state = {
            initialTimestamp: null,
            initialPosition: position,
            position: position,
            duration: duration
        };

        // Update right away if we don't have anything running.
        if (this._updateId === null) {
            // TODO: Consider wrapping this in a try/catch?
            this._userCallback(position, duration);
        }
        return this;
    };

    // Start the timer if it is not already running.
    ProgressTimer.prototype.start = function() {
        if (this._updateId === null) {
            this._updateId = this._schedule(0);
        }
        return this;
    };

    // Cancel the timer if it us currently tracking progress.
    ProgressTimer.prototype.stop = function() {
        if (this._updateId !== null) {
            this._cancel(this._updateId);

            // Ensure we correctly reset the initial position and timestamp.
            this.set(this._state.position, this._state.duration);
            this._updateId = null;  // Last step to avoid callback in set()
        }
        return this;
    };

    // Marks the timer as stopped, sets position to zero and duration to inf.
    ProgressTimer.prototype.reset = function() {
        return this.stop().set(0, Infinity);
    };

    // Calls the user callback with the current position/duration and then
    // schedules the next update run via _schedule if we haven't finished.
    ProgressTimer.prototype._update = function(timestamp) {
        var state = this._state;  // We refer a lot to state, this is shorter.

        // Make sure setTimeout has a timestamp and store first reference time.
        timestamp = timestamp || now();
        state.initialTimestamp = state.initialTimestamp || timestamp;

        // Recalculate position according to start location and reference.
        state.position = (
            state.initialPosition + timestamp - state.initialTimestamp);

        // Ensure callback gets an integer and that 'position <= duration'.
        var userPosisition = Math.min(
            Math.floor(state.position), state.duration);

        // TODO: Consider wrapping this in a try/catch?
        this._userCallback(userPosisition, state.duration);

        if (state.position < state.duration) {
            this._updateId = this._schedule(timestamp);  // Schedule update.
        } else {
            this._updateId = null;  // Unset since we didn't reschedule.
        }
    };

    return ProgressTimer;
}));