Stopwatch constructor to measure the elapsed time

Stopwatch.js

/** Stopwatch constructor to measure the elapsed time
 * @author Victor B - www.vitim.us
 */
function Stopwatch(){
    this.running = false;
    
    this.startTimestamp;
    this.endTimestamp;
}
Stopwatch.prototype.start = function(){
    this.running = true;
    return this.startTimestamp = this.endTimestamp = Date.now();
}
Stopwatch.prototype.stop = function(){
    this.running = false;
    this.endTimestamp = Date.now();
    return this.endTimestamp;
}
Stopwatch.prototype.elapsed = function(){
    if(this.running) this.endTimestamp = Date.now();
    return this.endTimestamp - this.startTimestamp;
}