54 lines
1.6 KiB
JavaScript
54 lines
1.6 KiB
JavaScript
"use strict";
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// Actual implementation of the Performance class.
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const clockIsAccurate = require("./clock-is-accurate");
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const calculateClockOffset = require("./calculate-clock-offset");
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const { hrtime, toMS } = require("./utils");
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const kTimeOrigin = Symbol("time origin");
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const kTimeOriginTimestamp = Symbol("time origin timestamp");
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class Performance {
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constructor() {
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// Time origin.
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const timeOrigin = hrtime();
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this[kTimeOrigin] = timeOrigin;
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if (clockIsAccurate) {
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// Let |t1| be the DOMHighResTimeStamp representing the high resolution Unix time at which the global monotonic
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// clock is zero. This has to be calculated for every Performance object to account for clock drifts.
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const t1 = calculateClockOffset();
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// Let |t2| be the DOMHighResTimeStamp representing the high resolution time value of the global monotonic clock
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// at global's time origin.
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const t2 = toMS(timeOrigin);
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// Return the sum of |t1| and |t2|.
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this[kTimeOriginTimestamp] = t1 + t2;
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} else {
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// Clock isn't accurate enough. Use millisecond accuracy per spec.
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const cur = Date.now();
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this[kTimeOriginTimestamp] = cur;
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}
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}
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// The timeOrigin getter actually returns the time origin timestamp, not the raw time origin.
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get timeOrigin() {
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return this[kTimeOriginTimestamp];
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}
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now() {
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const diff = toMS(hrtime(this[kTimeOrigin]));
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return clockIsAccurate ? diff : Math.round(diff);
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}
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toJSON() {
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return {
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timeOrigin: this.timeOrigin
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};
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}
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}
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module.exports = { Performance };
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