webapp | Meteor API Docs

The webapp package is what lets your Meteor app serve content to a web browser. It is included in the meteor-base set of packages that is automatically added when you run meteor create. You can easily build a Meteor app without it - for example if you wanted to make a command-line tool that still used the Meteor package system and DDP.

This package also allows you to add handlers for HTTP requests. This lets other services access your app’s data through an HTTP API, allowing it to easily interoperate with tools and frameworks that don’t yet support DDP.

webapp exposes the connect API for handling requests through WebApp.connectHandlers. Here’s an example that will let you handle a specific URL:

// Listen to incoming HTTP requests (can only be used on the server).
WebApp.connectHandlers.use('/hello', (req, res, next) => {
  res.writeHead(200);
  res.end(`Hello world from: ${Meteor.release}`);
});

Server

WebApp.connectHandlers([path], handler)

import { WebApp } from 'meteor/webapp'

(webapp/webapp_server.js, line 1157)

Arguments

path String

This handler will only be called on paths that match this string. The match has to border on a / or a ..

For example, /hello will match /hello/world and /hello.world, but not /hello_world.

handler connectHandlersCallback

A handler function that will be called on HTTP requests. See connectHandlersCallback

Server

connectHandlersCallback(req, res, next)

callback handler for WebApp.connectHandlers

Arguments

req Object: a Node.js IncomingMessage object with some extra properties. This argument can be used to get information about the incoming request.
res Object: a Node.js ServerResponse object. Use this to write data that should be sent in response to the request, and call res.end() when you are done.
next Function: Calling this function will pass on the handling of this request to the next relevant handler.

Serving a Static Landing Page

One of the really cool things you can do with WebApp is serve static HTML for a landing page where TTFB (time to first byte) is of utmost importance.

The Bundle Visualizer and Dynamic Imports are great tools to help you minimize initial page load times. But sometimes you just need to skinny down your initial page load to bare metal.

The good news is that WebApp makes this is really easy to do.

Step one is to create a your static HTML file and place it in the private folder at the root of your application.

Here’s a sample index.html you might use to get started:

<head>
    <title>Fast Landing Page</title>
    <meta charset="utf-8" />
    <meta http-equiv="x-ua-compatible" content="ie=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0 user-scalable=no" />   
    <link rel="stylesheet" href="path to your style sheet etc">
</head>

    <body>
        <!-- your content -->
    </body>

    <script>

    // any functions you need to support your landing page
 
    </script>

</html>

Then using the connectHandlers method described above serve up your static HTML on app-root/ page load as shown below.

/* global WebApp Assets */
import crypto from 'crypto'
import connectRoute from 'connect-route'

WebApp.connectHandlers.use(connectRoute(function (router) {
    router.get('/', function (req, res, next) {
        const buf = Assets.getText('index.html')

        if (buf.length > 0) {
            const eTag = crypto.createHash('md5').update(buf).digest('hex')

            if (req.headers['if-none-match'] === eTag) {
                res.writeHead(304, 'Not Modified')
                return res.end()
            }

            res.writeHead(200, {
                ETag: eTag,
                'Content-Type': 'text/html'
            })

            return res.end(buf);
        }

        return res.end('<html><body>Index page not found!</body></html>')
    })
}))

There are a couple things to think about with this approach.

We’re reading the contents of index.html using the Assets module that makes it really easy to read files out of the private root folder.

We’re using the connect-route NPM package to simplify WebApp route processing. But you can use any package you want to understand what is being requested.

And finally, if you decide to use this technique you’ll want to make sure you understand how conflicting client side routing will affect user experience.

Dynamic Runtime Configuration

In some cases it is valuable to be able to control the meteor_runtime_config variable that initializes Meteor at runtime.

Example

There are occasions when a single Meteor server would like to serve multiple cordova applications that each have a unique ROOT_URL. But there are 2 problems:

The Meteor server can only be configured to serve a single ROOT_URL.
The cordova applications are build time configured with a specific ROOT_URL.

These 2 conditions break autoupdate for the cordova applications. cordova-plugin-meteor-webapp will fail the update if the ROOT_URL from the server does not match the build time configured ROOT_URL of the cordova application.

To remedy this problem webapp has a hook for dynamically configuring __meteor_runtime_config__ on the server.

Dynamic Runtime Configuration Hook

WebApp.addRuntimeConfigHook(({arch, request, encodedCurrentConfig, updated}) => {
 // check the request to see if this is a request that requires
 // modifying the runtime configuration
  if(request.headers.domain === 'calling.domain') {
    // make changes to the config for this domain
    // decode the current runtime config string into an object
    const config = WebApp.decodeRuntimeConfig(current);
    // make your changes
    config.newVar = 'some value';
    config.oldVar = 'new value';
    // encode the modified object to the runtime config string
    // and return it
    return WebApp.encodeRuntimeConfig(config);
  }
  // Not modifying other domains so return undefined
  return undefined;
})

Server

WebApp.addRuntimeConfigHook(callback)

import { WebApp } from 'meteor/webapp'

(webapp/webapp_server.js, line 419)

Hook that calls back when the meteor runtime configuration, __meteor_runtime_config__ is being sent to any client.

returns: Object { stop: function, callback: function }

stop Function Call stop() to stop getting callbacks.
callback Function The passed in callback.

Arguments

callback addRuntimeConfigHookCallback: See addRuntimeConfigHookCallback description.

Server

addRuntimeConfigHookCallback(options)

Callback for addRuntimeConfigHook.

If the handler returns a falsy value the hook will not modify the runtime configuration.

If the handler returns a String the hook will substitute the string for the encoded configuration string.

Warning: the hook does not check the return value at all it is the responsibility of the caller to get the formatting correct using the helper functions.

addRuntimeConfigHookCallback takes only one Object argument with the following fields:

Arguments

options.arch String: The architecture of the client requesting a new runtime configuration. This can be one of web.browser, web.browser.legacy or web.cordova.
options.request Object: A NodeJs IncomingMessage https://nodejs.org/api/http.html#http_class_http_incomingmessage Object that can be used to get information about the incoming request.
options.encodedCurrentConfig String: The current configuration object encoded as a string for inclusion in the root html.
options.updated Boolean: true if the config for this architecture has been updated since last called, otherwise false. This flag can be used to cache the decoding/encoding for each architecture.

Additionally, 2 helper functions are available to decode the runtime config string and encode the runtime config object.

Server

WebApp.decodeRuntimeConfig(rtimeConfigString)

import { WebApp } from 'meteor/webapp'

(webapp/webapp_server.js, line 350)

Takes an encoded runtime string and returns a runtime configuration object.

Arguments

rtimeConfigString String

Server

WebApp.encodeRuntimeConfig(rtimeConfig)

import { WebApp } from 'meteor/webapp'

(webapp/webapp_server.js, line 339)

Takes a runtime configuration object and returns an encoded runtime string.

Arguments

rtimeConfig Object

Updated Runtime Configuration Hook

const autoupdateCache;
// Get a notification when the runtime configuration is updated
// for each arch
WebApp.addUpdatedNotifyHook(({arch, manifest, runtimeConfig}) => {
  // Example, see if runtimeConfig.autoupdate has changed and if so
  // do something
  if(!_.isEqual(autoupdateCache, runtimeConfig.autoupdate)) {
    autoupdateCache = runtimeConfig.autoupdate;
    // do something...
  }
})

Server

WebApp.addUpdatedNotifyHook(handler)

import { WebApp } from 'meteor/webapp'

(webapp/webapp_server.js, line 494)

Hook that runs when the meteor runtime configuration is updated. Typically the configuration only changes during development mode.

Arguments

handler addUpdatedNotifyHookCallback: The handler is called on every change to an arch runtime configuration. See addUpdatedNotifyHookCallback.

Server

addUpdatedNotifyHookCallback(options)

callback handler for addupdatedNotifyHook

Arguments

options.arch String: The architecture that is being updated. This can be one of web.browser, web.browser.legacy or web.cordova.
options.manifest Object: The new updated manifest object for this arch.
options.runtimeConfig Object: The new updated configuration object for this arch.

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