Convert `web3.eth` asynchronous calls into Rx observables.

rxifyWeb3.js

const Rx = require('rx');

module.exports = {
    rxify: function (web3) {
        // List synchronous functions masquerading as values.
        var syncGetters = {
            db: [],
            eth: [ "accounts", "blockNumber", "coinbase", "gasPrice", "hashrate",
                "mining", "protocolVersion", "syncing" ],
            net: [ "listening", "peerCount" ],
            personal: [ "listAccounts" ],
            shh: [],
            version: [ "ethereum", "network", "node", "whisper" ]
        };

        Object.keys(syncGetters).forEach(function(group) {
            Object.keys(web3[group]).forEach(function (method) {
                if (syncGetters[group].indexOf(method) > -1) {
                    // Skip
                } else if (typeof web3[group][method] === "function") {
                    web3[group][method + "Observable"] = Rx.Observable.fromNodeCallback(web3[group][method]);
                }
            });
        });
    },
};

You use it thus:

const Web3 = require("web3");
const web3 = new Web3(...);
const Rxifier = require("./rxifyWeb3.js");
Rxifier.rxify(web3);

web3.eth.getBlockNumberObservable()
    .flatMap(web3.eth.getBlockObservable)
    .subscribe(function (block) {
        console.log(block);
    });