You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
53 lines
1.6 KiB
53 lines
1.6 KiB
"use strict";
|
|
|
|
// Actual implementation of the Performance class.
|
|
|
|
const clockIsAccurate = require("./clock-is-accurate");
|
|
const calculateClockOffset = require("./calculate-clock-offset");
|
|
const { hrtime, toMS } = require("./utils");
|
|
|
|
const kTimeOrigin = Symbol("time origin");
|
|
const kTimeOriginTimestamp = Symbol("time origin timestamp");
|
|
|
|
class Performance {
|
|
constructor() {
|
|
// Time origin.
|
|
const timeOrigin = hrtime();
|
|
this[kTimeOrigin] = timeOrigin;
|
|
|
|
if (clockIsAccurate) {
|
|
// Let |t1| be the DOMHighResTimeStamp representing the high resolution Unix time at which the global monotonic
|
|
// clock is zero. This has to be calculated for every Performance object to account for clock drifts.
|
|
const t1 = calculateClockOffset();
|
|
|
|
// Let |t2| be the DOMHighResTimeStamp representing the high resolution time value of the global monotonic clock
|
|
// at global's time origin.
|
|
const t2 = toMS(timeOrigin);
|
|
|
|
// Return the sum of |t1| and |t2|.
|
|
this[kTimeOriginTimestamp] = t1 + t2;
|
|
} else {
|
|
// Clock isn't accurate enough. Use millisecond accuracy per spec.
|
|
const cur = Date.now();
|
|
this[kTimeOriginTimestamp] = cur;
|
|
}
|
|
}
|
|
|
|
// The timeOrigin getter actually returns the time origin timestamp, not the raw time origin.
|
|
get timeOrigin() {
|
|
return this[kTimeOriginTimestamp];
|
|
}
|
|
|
|
now() {
|
|
const diff = toMS(hrtime(this[kTimeOrigin]));
|
|
return clockIsAccurate ? diff : Math.round(diff);
|
|
}
|
|
|
|
toJSON() {
|
|
return {
|
|
timeOrigin: this.timeOrigin
|
|
};
|
|
}
|
|
}
|
|
|
|
module.exports = { Performance };
|