La guía para principiantes de Meteor

Meteor es una plataforma de aplicaciones web. Es una herramienta tanto para principiantes como para expertos, hace que sea muy fácil comenzar y proporciona un enorme ecosistema de bibliotecas que puede aprovechar.

Meteor es una plataforma de aplicaciones web.

Las aplicaciones web modernas pueden serextremadamente complicadoescribir. Especialmente para principiantes.

Meteor es una herramienta tanto para principiantes como para expertos, lo hacefácil de empezary proporciona un enorme ecosistema de bibliotecas que puede aprovechar.

JavaScript

Meteor ha sido uno de los primeros enfoques populares para usar JavaScript tanto en el cliente como en el servidor, sin problemas.

Junto conMongoDB, que es una base de datos que almacenaJSONobjetos y utiliza Javascript como lenguaje de consulta, hace que JavaScript sea omnipresente.

Meteor también se envía conMinimongoen la interfaz, que es una base de datos compatible con las API de MongoDB, completamente escrita en JavaScript.

Tiempo real

Meteor es conocido por sus funciones en tiempo real, pero ¿qué es exactamente el tiempo real? Suponga que desea crear una aplicación de chat. Meteor te ofrece funciones que son perfectas para eso.

¿Quiere crear una aplicación de comunicación interna? Perfecto también. ¿Una aplicación de gestión de proyectos? Básicamente, cualquier aplicación en la que los usuarios puedan ser notificados o las cosas deben actualizarse en función de las acciones de otros usuarios, o cosas de terceros como API cambian la información que se muestra, el usuario que ve la aplicación puede ser notificado de esos cambios de inmediato, de una manera bastante fácil. manera en comparación con otras soluciones.

Se siente rápido

Una cosa llamadaCompensación de latenciale ofrece un truco que permite que la interfaz se sienta muy rápido incluso si todavía necesita comunicarse con un servidor remoto. Y lo mejor de todo, es gratis para usted en términos de implementación, lo que significa que está respaldado en Meteor y no tiene que hacer nada para habilitarlo.

Fuente abierta

Por supuesto, Meteor es completamente de código abierto.

Es simple

Las cosas parecen muy simples en Meteor, porquesonsencillo.

Las cosas complicadas conducen a errores extraños o problemas difíciles más adelante. Meteor nos ofrece unAPI limpia y hermosay funcionalidad sobre la que construir.

Un gran sistema de paquetes

Lo bueno de Meteor es que, dado que puede alimentar tanto el frontend como el backend, y está profundamente integrado con la base de datos,tanto el código frontend como el backend se pueden poner en un solo paquetey trabaje sin problemas para nosotros en ambos lados. Es por eso que podemos agregar la administración de usuarios completa con una sola línea de código.

Cómo Meteor puede mejorar tu vida

Meteor te da unPlataforma Full-Stack, proporcionandotanto el marco del lado del cliente como el marco del lado del servidor. Es más, Meteor incluso le proporciona el canal de comunicación entre ellos. Se llamaDDP, y lo hablaremos más tarde.

Ya no es necesario unir diferentes marcos, lenguajes, herramientas y bases de código. Esto es enorme para el desarrollador independiente, las pequeñas empresas emergentes o incluso las organizaciones más grandes que no quieren perder tiempo y recursos haciendo las cosas más difíciles de lo que deberían ser.

Cuando Meteor podría no ser la mejor opción para ti

Sitios web de contenido estáticotienen otras plataformas mejores sobre las que basarse. Si solo necesita generar algo de HTML sin mucha interactividad, use un generador de sitio estático.

Meteoro en el momento de la escritura no admiteBases de datos SQL, lo que puede ser bueno en muchos casos, pero puede ser necesario en otros casos. Por supuesto, puede escribir sus propios procedimientos que utilicen datos SQL.

Los 7 principios de los meteoritos

Meteor se basa en los siguientes siete principios. Se enumeran en la documentación del proyecto y son principios fundamentales, por lo que los informaremos aquí.

Los principios siempre importan cuando se respetan en la vida cotidiana.

Datos en el cable

Meteor no envía HTML a través de la red. El servidor envía datos y deja que el cliente los renderice.

Un idioma

Meteor le permite escribir las partes del cliente y del servidor de su aplicación enJavaScript.

Base de datos en todas partes

Puede utilizar los mismos métodos para acceder a su base de datos desde el cliente o el servidor.

Compensación de latencia

En el cliente, Meteor obtiene datos previamente y simula modelos para que parezca que las llamadas al método del servidor regresan instantáneamente.

Reactividad de pila completa

En Meteor, el tiempo real es el predeterminado. Todas las capas, desde la base de datos hasta la plantilla, se actualizan automáticamente cuando es necesario.

Abraza el ecosistema

Meteor es de código abierto y se integra con marcos y herramientas de código abierto existentes.

Simplicidad es igual a productividad

La mejor manera de hacer que algo parezca simple es hacerlo realmente simple. La funcionalidad principal de Meteor tiene API limpias y clásicamente hermosas.

Procedimiento de instalación

En OSX y Linux, la instalación de Meteor es tan simple como escribir esto en la terminal del sistema operativo:

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

Install Meteor

¡Eso es!

Windows tiene su propio instalador oficial, así que compruébalo en el sitio oficial.

Primeros pasos con Meteor

Creemos la primera aplicación Meteor.

Abra la terminal del sistema operativo, vaya al directorio donde alojará el proyecto y escriba

meteor create hello-world

Create a Meteor app

Meteor creará la nueva aplicación para usted, en elhello-worlddirectorio.

Ahora entra en ese directorio y escribe

meteor

Esto activará el servidor web Meteor y podrá acceder a su primera aplicación Meteor apuntando su navegador ahttp://localhost:3000

Hello Meteor

Fue fácil, ¿verdad?

Recorrido de código

Repasemos el código de la aplicación para ver cómo funciona.

No se preocupe si las cosas no están muy claras en este momento, muchos conceptos se introducirán y explicarán más adelante.

Hace unos años, esta aplicación de muestra de Meteor habría contenido solo un archivo JavaScript, tanto para el cliente como para el servidor, usandoMeteor.isClientyMeteor.isServerpara comprobar si la aplicación se estaba ejecutando en el cliente o en el servidor.

La aplicación de muestra se alejó de este enfoque, y ¿cómo se haserver/main.jsarchivo y otros archivos enclient/.

client / main.html

Si abre elclient/main.htmlarchivo puede ver el código fuente de la aplicación:

<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 reconoce elheadybodyetiquetas y las coloca en el lugar correcto en el contenido de la página. Esto significa que al incluir unheadetiqueta, todo su contenido se agregará a la página "real"headetiqueta.

Lo mismo se aplica a labodyetiqueta. Son las dos etiquetas principales.

Todo el resto de la aplicación debe colocarse por separado.templateetiquetas.

El especial{{ }}los paréntesis que ves están definidos porBarras espaciadoras, que es un lenguaje de plantillas muy similar aBigote dalinianocon algunas características únicas que lo hacen perfecto para trabajar con Meteor

En el ejemplo del hola mundo,

{{> hello}}

incluye elhelloplantilla, y

{{counter}}

dentro dehelloplantilla busca el valor del contador en el contexto de la plantilla.

cliente / main.js

Este es el contenido de laclient/main.jsexpediente:

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); }, });

El código configura un ReactiveVar, unvariable reactiva. Una variable reactiva expone un setter y un getter. Al usar el setter, todas las funciones que están recuperando el valor usando get () recibirán una alerta cuando cambie su valor.

El valor de la variable reactiva se muestra en el HTML usando el{{counter}}fragmento, que llama alcounter()ayudante de plantilla que definimos aquí.

Primero inicializa esa variable a cero, y establece su valor para que se incremente cuando se hace clic en el botón en elhelloplantilla.

Para manejar los clics, actúa sobre los eventos delhelloplantilla. En este caso, interceptamos el clic en unbuttonElemento HTML. Cuando esto sucede, incrementa el valor de Session.counter.

En el código del servidor Meteor, enserver/main.js, hay unaMeteor.startupcall, que solo llama a la función pasada cuando Meteor está listo. Ahora no hay nada en él, pero veremos cómo esto puede ser útil más adelante.

El Meteor CLI

Al instalar Meteor, obtiene la CLI (utilidad de línea de comandos) llamadameteor.

Es una herramienta súper útil, ya la usó para crear la primera aplicación y, para empezar, solo necesitamos saber una pequeña fracción de lo que puede hacer.

Vamos a presentar los cuatro comandos más útiles que usará al comenzar con Meteor.

meteorito

Si dentro de un directorio vacío escribes

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>