Beginner's Guide to Meteor

Meteor is a web application platform. It is a tool for beginners and experts, it makes startup super easy, and provides a huge library ecosystem that can be used

Meteor is a web application platform.

Modern web applications canExtremely complicatedTo write. Especially for beginners.

Meteor is a tool for beginners and experts, it makeseasy to use, And provide a huge library ecosystem that you can use.

JavaScript

The Meteor method is one of the first popular methods to seamlessly use JavaScript on the client and server.

PlusMongoDB, This is a database for storingJSON formatObject, and use Javascript as the query language, it makes JavaScript ubiquitous.

Meteor also comes withMini MongoIn the front-end, this is a front-end database compatible with MongoDB API, written entirely in JavaScript.

real time

Meteor is famous for its real-time capabilities, but what exactly is real-time? Suppose you want to create a chat application. Meteor provides you with perfect functions.

Want to create an internal communication application? so perfect. Project management application? Basically, any application that can notify users or update things based on other user actions, or third-party things such as APIs, can change the displayed information, and it is easy to immediately notify these changes to the viewing application Of users compared with other solutions.

Feel fast

One calledDelay compensationProvide you with a trick, even if the interface still needs to communicate with the remote server, you can make the interface disappear quickly. Most importantly, it is free to you in terms of implementation, which means that it is already supported in Meteor and you don't need to do anything to enable it.

Open source

Of course, Meteor is completely open source.

this is very simple

Things seem very simple in Meteor, because theyYessimple.

Complicated things will lead to strange errors or difficult problems later. Meteor provides us withClean and beautiful APIand function.

Excellent packaging system

The coolest thing about Meteor is that since it can support both front-end and back-end, and is deeply integrated with the database,Both front-end and back-end code can be placed in one package, And work seamlessly for us between the two parties. This is why we can add complete user management with one line of code.

How meteors improve lives

Meteor to youFull stack platformBy providingClient-side framework and server-side framework. More importantly, Meteor even provides you with a communication channel between the two. CalledDDP, We will discuss it later.

You no longer need to glue together different frameworks, languages, tools and code bases. This is huge for independent developers, small startups, and even larger organizations who don’t want to waste time and resources making things more difficult than they should.

When the meteor may not be for you

Static content websiteThere are other better platforms that can be built. If you only need to output some HTML without much interactivity, please use a static website generator.

As of writing, Meteor does not supportSQL database, Which may be a good thing in many situations, but they may be needed in other situations. Of course, you can write your own procedures for using SQL data.

The Seven Principles of Meteor

Meteor is based on the following seven principles. They are listed in the project documentation, they are basic principles, so we will report here.

Principles are always important when they are respected in daily life.

Online data

Meteor will not send HTML over the network. The server sends the data and lets the client present it.

A language

With Meteor, you can write the client and server parts of your application in the following locations:JavaScript.

The database is everywhere

You can use the same method to access the database from the client or server.

Delay compensation

On the client side, Meteor will prefetch the data and simulate the model to make it look like the server method call returns immediately.

Full reactor reactivity

In Meteor, real time is the default setting. All layers from the database to the template are automatically updated when necessary.

Embrace the ecology

Meteor is open source and integrated with existing open source tools and frameworks.

Simplicity equals productivity

The best way to make something seem simple is to make it actually simple. The main function of Meteor has a clean, classic and beautiful API.

installation steps

On OSX and Linux, installing Meteor is as easy as typing the following commands in the "operating system" terminal:

curl https://install.meteor.com/ | sh

Install Meteor

That's it!

Windows has its own official installer, so please check on the official website.

Meteor's first step

Let's create the first Meteor application.

Open the operating system terminal, enter the directory where you will host the project, and type

meteor create hello-world

Create a Meteor app

Meteor will create a new app for you in your phonehello-worldtable of Contents.

Now go into that directory and enter

meteor

This will start the Meteor web server, and you can access your first Meteor application by pointing your browser to it.http://localhost:3000

Hello Meteor

It's simple, right?

Code walkthrough

Let's walk through the application code to understand how it works.

If it’s not clear yet, don’t worry, many concepts will be introduced and explained later.

A few years ago, this Meteor sample application only contained a JavaScript file for the client and server, usingMeteor.isClientwithMeteor.isServerCheck whether the application is running on the client or the server.

The sample application got rid of this method and howserver/main.jsFiles, and other filesclient/.

client/main.html

If you openclient/main.htmlFile, you can see the source code of the application:

<head>
  <title>hello-world</title>
</head>

<body> <h1>Welcome to Meteor!</h1>

{{> hello}} {{> info}} </body>

<template name=“hello”> <button>Click Me</button> <p>You’ve pressed the button {{counter}} times.</p> </template>

<template name=“info”> <h2>Learn Meteor!</h2> <ul> … </ul> </template>

Meteor recognizesheadwithbodyMark and place it in the correct position in the content of the page. This means by including aheadLabel, all of which will be added to the "real" pageheadlabel.

The same situation applies tobodylabel. They are the two main tags.

All remaining applications must be placed in a separate locationtemplatelabel.

special{{ }}The brackets you see are caused byspace bar, Which is a template language, andhandlebarHas some unique features, making it a perfect match with Meteor

In the hello-world example,

{{> hello}}

includehelloTemplates, and

{{counter}}

InsidehelloThe template looks up the counter value in the template context.

Client/main.js

This is the contentclient/main.jsfile:

import { Template } from 'meteor/templating';
import { ReactiveVar } from 'meteor/reactive-var';

import ‘./main.html’;

Template.hello.onCreated(function helloOnCreated() { // counter starts at 0 this.counter = new ReactiveVar(0); });

Template.hello.helpers({ counter() { return Template.instance().counter.get(); }, });

Template.hello.events({ ‘click button’(event, instance) { // increment the counter when button is clicked instance.counter.set(instance.counter.get() + 1); }, });

The code sets up a ReactiveVar,Response variable. The reaction variable exposes a setter and a getter. By using the setter, when its value changes, get() will be used to retrieve all functions that use the value.

Use of the value of the reaction variable{{counter}}Fragment, this is calledcounter()The template helper we defined here.

It first initializes the variable to zero, and then sets its value to increment when the button is clicked in the button.hellotemplate.

To handle clicks, you need tohellotemplate. In this case, we blocked the clickbuttonHTML elements. When this happens, you increase the Session.counter value.

In the meteor server code,server/main.js, There is aMeteor.startupCall, it only calls the passed function when Meteor is ready. There is no content right now, but we will see how it is useful later.

Meteor CLI

When you install Meteor, you will get the namemeteor.

This is a very useful tool, you have already used it to create your first application, and from the beginning we only need to know a small part of what it can do.

Let us introduce the four most useful commands from Meteor.

meteor

If you are in an empty directory, type

meteor

you’ll get an error because Meteor was not initialized in that directory.

If you instead type meteor in a folder that has a Meteor project already created (see meteor create here below), Meteor will start up and create the server, initialize the database and you’ll be able to open the Meteor website.

meteor create

If inside a directory you type

meteor create my_app_name

Meteor will initialize a new Meteor project in a subfolder named my_app_name.

meteor add

Inside your Meteor project already initialized, calling

meteor add package_name

will lookup the package_name package and will install it in the current project.

You can run this command in a separate terminal window while the Meteor app is running, and you’ll get the package functionality without the need to restart the Meteor server.

meteor remove

Inside your Meteor project already initialized, calling

meteor remove package_name

will remove the package with that name from your project.

Isomorphic

The term isomorphic identifies a framework where client-side code and server-side code are written in the same language. This implies that any piece of code could run both on the server and on the client, unless it’s tied to a context-specific action.

In the past 10 years Web Applications have been built by clearly separating the server and the client code. Server code run PHP, Ruby, Python code. That code could never work on the frontend-side, because the browser does not support those languages.

Browsers are only capable of executing code written in JavaScript.

With the meteoric rise of Node.js in the last few years, and what was built on top, now we have the chance to build an entire application in the same language: JavaScript.

Meteor takes the isomorphic concept even further, by transparently running every file in your project, unless you don’t want it to do it, on both sides of the platform, doing different things based on the context, clearly explained by the Meteor documentation.

This is an amazing opportunity and advantage that Meteor enables by building a “super-platform” on top of Node.js and the Browser platforms, enabling you to build applications faster and better than ever.

Isomorphic refers to JavaScript code that runs with little to no modifications on the client and on the server. It’s code that takes care of both what runs inside the browser, and the what runs on the server.

Meteor is an isomorphic framework. This is great because we can write concise applications that now even share some pieces of code between client and server code.

It enables you to become a full-stack developer, because you no longer need to deeply know two separate stacks to work on both sides of the application.

The classical example is the one of an HTTP request. On the browser you’d do an AJAX call. On the server you’d use your stack-specific code.

Using Meteor, you can use the same function HTTP.get() provided by the http package, on both sides, just like when you install the Axios library.

Meteor.isServer, Meteor.isClient

Meteor exposes two boolean variables to determine where the code is running:

  • Meteor.isServer
  • Meteor.isClient


Put them inside an if statement to run some code part just on one side of the platform.

For example:

if (Meteor.isClient) {
  alert('Hello dear user!')
} else if (Meteor.isServer) {
  //running server-side
}

Special directories

Putting lots of Meteor.isServer and Meteor.isClient checks in the application is not ideal of course.

First, the code can quickly grow complicated and not nice to read. Second, even the server code is sent to the client. This is bad because you’d better keep server-side code private, and also because you send unnecessary code which slows down loading times.

That’s why Meteor has two special folders that automatically take care of the distinction for us: client and server

Whatever you put in the client directory is not loaded on the server side.

Whatever you put in the server directory is not sent to the client.

Another advantage of keeping this distinction is that assets put in the client folders are never taken into consideration during the build phases.

Session variables and template helpers

Here’s a simple example on combining Session variables and template helpers to achieve a simple case of selecting the current comment selected in a list.

In our template.html file:

<template name="main">
  {{#each comments}}
    {{> comment}}
  {{/each}}
</template>

<template name=“comment”> <div class="{{#if selected}}selected{{/if}}"> <p>{{this.comment}}</p> </div> </template>

In template.js:

Session.set('selectedComment', null)

Template.main.helpers({ comments: function() { return Comments.find() } })

Template.comment.helpers({ selected: function() { return Session.equals(‘selectedComment’, this._id) } })

Template.comment.events({ ‘click div’ : function(e, t) { Session.set(‘selectedComment’, this._id) } })

In this case any time I click a comment, that comment becomes the selected comment, and we can show it full-size, fetch the other comments made by the user or do some other fancy stuff.

Reactive programming

First, a clarification: Meteor’s reactivity has nothing to do with React, the other very popular JavaScript framework.

What is reactive programming, you say? Reactive programming is a programming paradigm.

Reactive programming is nothing new, nor something that Meteor introduced. But, what Meteor did was making reactive programming easy to use.

Actually, you’re most probably already using reactive programming without even knowing about it.

What is reactive programming

Reactive programming allows you to write code that automatically refreshes and re-calculates functions and values when something that you depend on changed.

For example, data in the database changed? You need to re-display it in the client.

That variable that counts the number of comments changed because you added a comment? Everything that depends on it, or shows it, must react to that change and re-compute the values.

That works by having Reactive Sources. The database for example is a reactive source. When something changes inside it, it notifies the JavaScript variables that depend on those changes. Those variables are invalidated and must be recalculated according to the new data available.

Reactive sources

Meteor has a list of things that are reactive, and those drive the entire application. Not everything is reactive, just those things listed here:

  • Reactive variables, defined using new ReactiveVar()

  • The data coming from the database is a reactive data source, because by subscribing to a publication you get a cursor, and that cursor is reactive. Any change to the collection represented by the cursor will trigger a recomputation of anything that uses it.

  • Talking about subscriptions, when a subscription is available on the client its .ready() method is called. That is a reactive data source.

  • Session variables are a reactive data source. When one changes a session variable by using .set(), everything that depends on those will be recalculate or re-rendered.

  • The user methods Meteor.user() and Meteor.userId() are a reactive data source.

  • Meteor.status(), which is a client-side method that returns the current client-server connection status, is a reactive data source.

  • Meteor.loggingIn(), which returns true if the user is currently doing a login, is a reactive data source.

Reactive computations

Whatever changes upon a reactive source change is a reactive computation. It’s some piece of code, a function, that needs to run again when a reactive source it depends on changes.

An example of reactive computation is the template helpers: every time a reactive data source that involves a template helper changes, the template re-renders it.

Defining your own reactive computations

You can define your own reactive computations, and react when something changes upstream, by using Tracker.autorun().

This function:

Tracker.autorun(function () {
  var currentPage = Session.get('currentPage')
  alert("The current page is " + currentPage)
})

Will trigger an alert whenever you call Session.set('currentPage', 'whatever') without you needing to add callbacks or other observers.

Meteor Publications

One of the key features of Meteor is provided by the data layer.

Since Meteor manages both the server and the client, I can explain the concept in this way:

  • The server creates a publication
  • The client subscribes to that publication
  • Meteor keeps everything in sync

The server can precisely determine what each client will see. Each publication can be tailored upon parameters and user permissions.

Let’s do a simple Pub/Sub introduction on standard MongoDB collections.

Server publication

Here’s an example of a server code creating a publication for comments that have been approved:

//server-side code
Meteor.publish('comments', () => {
  return Comments.find({ approved: true })
})

Or we want to create a publication for comments made on a specific article:

Meteor.publish('comments', (articleId) => {
  return Comments.find({ articleId: articleId })
})

The publish function is called every time a client subscribes.

Client subscription

On the client the code is very easy. For example, let’s subscribe to all comments:

Meteor.subscribe('comments')

Let’s instead subscribe to comments made on the current article:

const articleId = 23
Meteor.subscribe('comments', articleId)

Once the subscribe method has been called, Meteor fills the client-side Minimongo (the MongoDB instance running on the client) with the data you chose to sent it.

Typically the client-side database only gets some records, the minimum amount needed to initialize and work. You don’t replicate the whole server-side Mongo collection content of course, but you request data as needed.

Autopublish

Meteor makes it very easy for us to start diving into a project without worrying at all about publications and subscriptions.

It does this by including the autopublish package in every new project. That that packages does is, it automatically creates a pub/sub for each collection we have defined, syncing all the data available from server to client.

When you’ll reach the phase when you need more control on the data available to each user or view, you’ll just remove the autopublish package and you’ll manually define what you need.

Minimongo

Minimongo is your best friend when developing in Meteor. Ok, if you feel you have lots of best friends when using Meteor, I feel the same. Everything in Meteor is provided to ease your life.

Minimongo, in particular, is a frontend implementation of MongoDB. You might say.. what? Why do I need another database?

MongoDB: The Meteor Database

As of writing, Meteor has just one officially supported database: MongoDB.

You may wonder why. First, let me clarify: you can actually use any database you want, but to enjoy at 100% the marvels of Meteor you need to use Mongo. There are currently community projects that are working towards adding support for many other databases.

MongoDB in two words

MongoDB is a document-based database. It features high performance, high availability, easy scalability. It stores its documents in database collections. A document is a set of key-value pairs (JSON), and it has a dynamic schema. This means that each document does not need to have the same set of fields, but you have a great freedom in managing data.

Meteor and MongoDB

As said, a MongoDB document is a JSON object. Meteor Collections are directly related to MongoDB collections, and the Meteor internals make sure that when data changes in a MongoDB Collection tracked by Meteor, the Meteor Collection is updated too.

Minimongo

In short, in Meteor you typically create a collection, and that collection is available on both client and server code. When you do some database query or database processing, you don’t “think” whether you should do that operation on the client-side database, or the server-side database: to a certain extent, they’re mostly the same thing. And they talk to each other transparently.

This means that when the server-side database (MongoDB) is updated by someone else or something happens in the app you’re using, or even you add something in a second browser window.. everything that’s stored in the database that interests your current session is pushed by the server MongoDB to the Minimongo running inside your browser.

The same happens for the opposite: you push a post to the Posts collection? Minimongo is updated immediately, while Meteor pushes the update to the MongoDB database server side.

This has the nice effect of making your changes, your pages and interactions feel immediate to the user.

Minimongo is a MongoDB client-side clone

Minimongo tries to perfectly emulate a subset of MongoDB. You can insert data, remove data, search, sort, update.. with the same exact MongoDB APIs.

This means you can also easily port some parts of your code from the server to the client-side very easily when it makes sense.

Client-side storage facility

With Minimongo you have a fantastic client-side storage that you can query using the MongoDB Query functionalities.

You can of course create instances of a Minimongo collection just client-side, when you don’t have the need to sync a collection to the server.

Not only, you can observe for database changes, and your interface can react to those changes easily.

Latency Compensation

Latency Compensation is part of the Meteor Principles. There, it’s described in this way: on the client, Meteor prefetches data and simulates models to make it look like server method calls return instantly.

What does it mean?

On a typical Web Application, when you do some kind of action, the action is passed to the server to be processed, and then you need to wait until the server responds, and then changes are applied to the page you’re interacting with.

More modern applications rely on AJAX to provide a better turnaround and avoid refreshing a page on every action, but still many apps rely on the server response prior to taking any action. Better apps introduce some sort of latency compensation, but it’s a manual process.

Meteor introduces the concept of Latency Compensation deep into his philosophy and it’s enabled by default, without you needing to do anything special to work with it.

For example when you add an item to a collection, meanwhile the item will be sent to the server, it’s already added to the collection view on your page.

It feels better, because the app feels immediately responsive (it is).

If there is an error you’ll be notified later and you have the opportunity to handle things in the best way for each situation.

Meteor Collections

An application typically needs to display data of some sort.

Be it messages, comments, posts, books, addresses, pictures.. everything is a collection of something.

Meteor being deeply integrated with MongoDB takes the Mongo database collection concept and takes it to the application level.

In both the client and server contexts, you’ll typically interact with data by interacting with data collections.

How does it work?

Create your first collection

Messages = new Mongo.Collection('messages')

This defines a global variable messages, which will be visible across the entire App on client and server.

This code needs to run on both the client and the server, so you’ll put it for example under collections/messages.js.

While the code running in the two environments is the same, what it does is different:

  • on the server it creates a Mongo collection if it’s not already existing, and then it will load the cursor in the Messages variable
  • on the client it will instantiate a Minimongo local collection. The app once instantiated will link that to the server-side collection, and will automatically keep them in sync.

Adding items to a collection

You’ll be able to insert items into a collection using the .insert() method on the collection cursor:

Messages.insert({message: "Hi"})

Showing the collection in the template

In a template you can use the {{#each}} Spacebars helper to navigate the collection and print all values stored in it:

<template name="messages">
  {{#each messages}}
    {{message}}
  {{/each}}
</template>