var ClockSkew = require('clockskew/client');
// or just include the file 

var clockSkew = new ClockSkew({
    // REQUIRED :
    getServerTime: ClockSkew.getSocketTime('ws://...'),
    // or use HTTP protocol
    getServerTime: ClockSkew.getHttpTime.bind(null,'http://'),
    // or use Firebase
    getServerTime: ClockSkew.getFirebaseTime.bind(null,'https://xxx.firebaseio.com/timestamp')

    // OPTIONAL:
    getTime: function(){...}, // get local time in ms.
    timeout: 10000, // ping timeout
    interval: 1000, // ping interval
    history: 10, 
    tolerance: 2, // is standard deviation of last `history` average skew is less then tolerance, wait longer before pinging.
    waitInteval: 30000, // wait interval
    minSkewValues: 5, // minimum values before averaging
    minRttValues: 5 // minimum Round-Trip-Time values before rejecting RTTs that are more than 1 standard deviation slower
    setTimeout: ... // custom setTimeout Implementation
    clearTimeout: ... // custom clearTimeout implementation
    onSkew: function(skew) { // do stuff },
});

clockSkew.start();
clockSkew.stop();
clockSkew.skew;