I am running 2 images with Docker Compose and I am having trouble hitting the localhost from my Mac. I am exposing ports 3000. Am I missing something?

I am building a Node/Mongo app using Docker and I am having trouble hitting my localhost from my host computer running MacOs when I run docker-compose up. Using postman or curl -i localhost:3000 returns nothing. I have also tried inspecting the container and connecting with that ip. What am I doing wrong? Thanks!

docker-compose.yml:

version: "2"
services:
  web:
    build: .
    ports:
      - "3000:3000"
    volumes:
      - .:/app
    env_file:
      - todoListDocker.env
    links:
      - mongo

mongo:
    image: mongo
    environment:
      - MONGO_INITDB_ROOT_USERNAME=root
      - MONGO_INITDB_ROOT_PASSWORD=tWwp3Fm4hZUsaLw4
    volumes:
      - mongo:/data/db
    ports:
      - "27017:27017"
    env_file:
      - todoListDocker.env

volumes:
  mongo:

Dockerfile:

FROM node:boron

MAINTAINER Clinton Medbery <clintomed@gmail.com>

RUN ["apt-get", "update"]
RUN ["apt-get", "install", "-y", "vim"]

RUN mkdir - p /app
WORKDIR /app

COPY package.json /app

RUN npm install

COPY . /app
EXPOSE 3000

CMD ["npm", "start"]

Index.js:

const express = require('express');
const morgan = require('morgan');
const bodyParser = require('body-parser');
const mongoose = require('mongoose');

var app = express();

var router = require('./services/router');

//Use ENV Variables
console.log("Connecting to Mongo");
mongoose.connect('mongodb://root:tWwp3Fm4hZUsaLw4@mongo:27017');
// mongoose.connect('mongodb://localhost:todoList/todoList');

console.log("Connected to Mongo");


app.use(morgan('combined'));
app.use(bodyParser.json());
app.use('/v1', router);

var PORT = process.env.PORT || 3000;
var HOST = process.env.HOST || '127.0.0.1';

app.get('/hello', function (req, res) {
    console.log("Hello World");
    res.send({hello:'Hello World!'});
});

console.log('Listening on port ', HOST, PORT);
app.listen(PORT, HOST);

via ShadyAmoeba