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122 lines
3.4 KiB
JavaScript
122 lines
3.4 KiB
JavaScript
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/**
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* Mimic the Timer class with external control of the "time" value, allowing tests to run more quickly and
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* reliably. Multiple instances of this class operate independently: they may report different time values, and
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* advancing one timer will not trigger timeouts set on another.
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*/
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class MockTimer {
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/**
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* Creates an instance of MockTimer.
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* @param {*} [nowObj=null] - alert the caller that this parameter, supported by Timer, is not supported here.
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* @memberof MockTimer
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*/
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constructor (nowObj = null) {
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if (nowObj) {
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throw new Error('nowObj is not implemented in MockTimer');
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}
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/**
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* The fake "current time" value, in epoch milliseconds.
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* @type {number}
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*/
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this._mockTime = 0;
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/**
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* Used to store the start time of a timer action.
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* Updated when calling `timer.start`.
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* @type {number}
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*/
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this.startTime = 0;
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/**
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* Array of pending timeout callbacks
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* @type {Array.<Object>}
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*/
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this._timeouts = [];
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}
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/**
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* Advance this MockTimer's idea of "current time", running timeout handlers if appropriate.
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* @param {number} delta - the amount of time to add to the current mock time value, in milliseconds.
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* @memberof MockTimer
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*/
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advanceMockTime (delta) {
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if (delta < 0) {
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throw new Error('Time may not move backward');
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}
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this._mockTime += delta;
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this._runTimeouts();
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}
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/**
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* @returns {number} - current mock time elapsed since 1 January 1970 00:00:00 UTC.
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* @memberof MockTimer
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*/
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time () {
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return this._mockTime;
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}
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/**
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* Returns a time accurate relative to other times produced by this function.
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* @returns {number} ms-scale accurate time relative to other relative times.
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* @memberof MockTimer
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*/
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relativeTime () {
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return this._mockTime;
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}
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/**
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* Start a timer for measuring elapsed time.
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* @memberof MockTimer
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*/
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start () {
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this.startTime = this._mockTime;
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}
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/**
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* @returns {number} - the time elapsed since `start()` was called.
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* @memberof MockTimer
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*/
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timeElapsed () {
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return this._mockTime - this.startTime;
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}
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/**
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* Call a handler function after a specified amount of time has elapsed.
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* Guaranteed to happen in between "ticks" of JavaScript.
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* @param {function} handler - function to call after the timeout
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* @param {number} timeout - number of milliseconds to delay before calling the handler
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* @memberof MockTimer
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*/
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setTimeout (handler, timeout) {
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this._timeouts.push({
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time: this._mockTime + timeout,
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handler
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});
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this._runTimeouts();
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}
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/**
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* Run any timeout handlers whose timeouts have expired.
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* @memberof MockTimer
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*/
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_runTimeouts () {
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const ready = [];
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const waiting = [];
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// partition timeout records by whether or not they're ready to call
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this._timeouts.forEach(o => {
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const isReady = o.time <= this._mockTime;
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(isReady ? ready : waiting).push(o);
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});
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this._timeouts = waiting;
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// next tick, call everything that's ready
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global.setTimeout(() => {
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ready.forEach(o => o.handler());
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}, 0);
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}
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}
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module.exports = MockTimer;
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