pi-event-emitter.js

'use strict';

const Big = require('big.js');
const EventEmitter = require('events');

/**
 * An EventEmitter that emits subsequent approximations of number Pi.
 * @extends external:EventEmitter
 */
class PiEmitter extends EventEmitter {
  constructor() {
    super();
    this._iteration = new Big(0);
    this._inside = new Big(0);
    this._samplesPerEvent = new Big(1000000);
    this._piInterval = null;
  }

  start() {
    const self = this;
    // Execute the computation task periodically to avoid starving the CPU:
    self._piInterval = setInterval(function() {
      const start = self._iteration;
      const limit = start.plus(self._samplesPerEvent);
      // Create a local counter to speed up computation (big.js is pretty slow):
      let inside = 0;
      // Check how many random points are inside the 1x1 circle:
      for (let i = start; i.lt(limit); i = i.plus(1)) {
    		let x = Math.random() * 2 - 1;
    		let y = Math.random() * 2 - 1;
    		if ((x*x + y*y) < 1) {
    				inside = inside + 1;
    		}
    	}
      self._iteration = limit;
      self._inside = self._inside.plus(inside);
      const bestPiValue = self._inside.times(4).div(self._iteration);

      // Emit the result:
      self.emit('pi', bestPiValue);
    }, 1);
  }
}

const myPi = new PiEmitter();
myPi.on('pi', function(piValue) {
  console.log('best Pi value: %s', piValue);
});
myPi.start();

pi-rx.js

'use strict';

const Big = require('big.js');
const Observable = require('rxjs/Rx').Observable;

/**
 * An Observable stream of Pi approximations.
 * @extends external:EventEmitter
 */
class PiRx {
  constructor() {
    this._iteration = new Big(0);
    this._inside = new Big(0);
    this._samplesPerEvent = new Big(1000000);
    this._piInterval = null;
  }

  getPiStream() {
    const self = this;
    // Execute the computation task periodically to avoid starving the CPU:
    return Observable.create(function(observable) {
      self._piInterval = setInterval(function() {
        const start = self._iteration;
        const limit = start.plus(self._samplesPerEvent);
        // Create a local counter to speed up computation (big.js is pretty slow):
        let inside = 0;
        // Check how many random points are inside the 1x1 circle:
        for (let i = start; i.lt(limit); i = i.plus(1)) {
          let x = Math.random() * 2 - 1;
          let y = Math.random() * 2 - 1;
          if ((x*x + y*y) < 1) {
              inside = inside + 1;
          }
        }
        self._iteration = limit;
        self._inside = self._inside.plus(inside);
        const bestPiValue = self._inside.times(4).div(self._iteration);

        // Emit the result:
        observable.next(bestPiValue);
      }, 1);
    });
  }
}

const myPi = new PiRx();
const myPiStream = myPi.getPiStream();
myPiStream.subscribe(function(piValue) {
  console.log('best Pi value: %s', piValue);
});