Socket.ioをAngularJS1.xの$qでPromisifyした

サービスの定義

socket.js

app.factory('Socket', function($rootScope, $q) {
  const makeAsyncCb = (cb)=> (data)=> {
    const deferred = $q.defer();
    cb(data, (data, cb)=> deferred.resolve([data, makeAsyncCb(cb)]));
    return deferred.promise;
  };

  return class Socket {
    constructor() {
      this.socket = io();
    }
    on(name, fn) {
      this.socket.on(name, fn && ((...args)=> {
        $rootScope.$apply(()=> fn(...args));
      }));
    }
    onAsync(name, fn) {
      this.socket.on(name, (data, cb)=> {
        fn($q.resolve([data, makeAsyncCb(cb)]));
      });
    }
    emit(name, arg, fn) {
      this.socket.emit(name, arg, fn && ((...args)=> {
        $rootScope.$apply(()=> fn(...args));
      }));
    }
    emitAsync(name, arg) {
      const deferred = $q.defer();
      this.socket.emit(name, arg, (data, cb)=> {
        deferred.resolve([data, makeAsyncCb(cb)]);
      });
      return deferred.promise;
    }
  };
});

使う時

my-controller.js

app.controller('myController', function(Socket) {
  const socket = new Socket();

  socket.onAsync('greeting-from-server', promise => {
    promise.then(([data, cbAsync])=> {
      console.log(data);
      return cbAsync('Nice to meet you, too.');
    }).then(([data, cbAsync])=> {
      console.log(data);
    });
  });

  socket.emitAsync('greeting-from-client', 'Hello!').then(([data, cbAsync])=> {
    console.log(data);
    return cbAsync('Have a nice day.');
  }).then(([data, cbAsync])=> {
    console.log(data);
  });
});