scratch-vm/src/util/timer.js
Tim Mickel ebbfe881db Augment Timer with documentation and self.performance.now (#163)
* Augment Timer with documentation and `self.performance.now`

* Add undefined check for `self`.
2016-09-12 13:09:01 -04:00

70 lines
1.7 KiB
JavaScript

/**
* @fileoverview
* A utility for accurately measuring time.
* To use:
* ---
* var timer = new Timer();
* timer.start();
* ... pass some time ...
* var timeDifference = timer.timeElapsed();
* ---
* Or, you can use the `time` and `relativeTime`
* to do some measurement yourself.
*/
/**
* @constructor
*/
function Timer () {}
/**
* Used to store the start time of a timer action.
* Updated when calling `timer.start`.
*/
Timer.prototype.startTime = 0;
/**
* Return the currently known absolute time, in ms precision.
* @returns {number} ms elapsed since 1 January 1970 00:00:00 UTC.
*/
Timer.prototype.time = function () {
if (Date.now) {
return Date.now();
} else {
return new Date().getTime();
}
};
/**
* Returns a time accurate relative to other times produced by this function.
* If possible, will use sub-millisecond precision.
* If not, will use millisecond precision.
* Not guaranteed to produce the same absolute values per-system.
* @returns {number} ms-scale accurate time relative to other relative times.
*/
Timer.prototype.relativeTime = function () {
if (typeof self !== 'undefined' &&
self.performance && 'now' in self.performance) {
return self.performance.now();
} else {
return this.time();
}
};
/**
* Start a timer for measuring elapsed time,
* at the most accurate precision possible.
*/
Timer.prototype.start = function () {
this.startTime = this.relativeTime();
};
/**
* Check time elapsed since `timer.start` was called.
* @returns {number} Time elapsed, in ms (possibly sub-ms precision).
*/
Timer.prototype.timeElapsed = function () {
return this.relativeTime() - this.startTime;
};
module.exports = Timer;