Mu Javascript template

Template for writing mu.semte.ch services in JavaScript using Express 4

Getting started

Create a new folder. Add the following Dockerfile:

FROM semtech/mu-javascript-template
MAINTAINER Aad Versteden <[email protected]>

Create your microservice in app.js:

import { app, query, errorHandler } from 'mu';

app.get('/', function( req, res ) {
  res.send('Hello mu-javascript-template');
} );


app.get('/query', function( req, res ) {
  var myQuery = `
    SELECT *
    WHERE {
      GRAPH <http://mu.semte.ch/application> {
        ?s ?p ?o.
      }
    }`;

  query( myQuery )
    .then( function(response) {
      res.send( JSON.stringify( response ) );
    })
    .catch( function(err) {
      res.send( "Oops something went wrong: " + JSON.stringify( err ) );
    });
} );

app.use(errorHandler);

Check Express' Getting Started guide to learn how to build a REST API in Express.

Requirements

• database link: You need a link to the database which exposes a SPARQL endpoint on http://database:8890/sparql. In line with other microservices.

Imports

The following importable variables are available:

• app: The Express application on which routes can be added
• query(query) => Promise: Function for sending queries to the triplestore
• update(query) => Promise: Function for sending updates to the triplestore
• uuid() => string: Generates a random UUID
• errorHandler(err, req, res, next): Error handling middleware function for Express. It needs to be loaded at the end.
• sparql: Template tag to create queries with interpolated values
• sparqlEscapeString(value) => string: Function to escape a string in SPARQL
• sparqlEscapeUri(value) => string: Function to escape a URI in SPARQL
• sparqlEscapeInt(value) => string: Function to escape an integer in SPARQL
• sparqlEscapeFloat(value) => string: Function to escape a float in SPARQL
• sparqlEscapeDate(value) => string: Function to escape a date in SPARQL. The given value is passed to the Date constructor.
• sparqlEscapeDateTime(value) => string: Function to escape a datetime in SPARQL
• sparqlEscapeBool(value) => string: Function to escape a boolean in SPARQL. The given value is evaluated to a boolean value in javascript. E.g. the string value '0' evaluates to false in javascript.
• sparqlEscape(value, type) => string: Function to escape a value in SPARQL according to the given type. Type must be one of 'string', 'uri', 'int', 'float', 'date', 'dateTime', 'bool'.

You can either import specific attributes from the mu library, or import the whole mu object.

An example of importing specific variables:

import { app, query } from 'mu';

app.get('/', function( req, res ) {
  res.send('Hello mu-javascript-template');
} );

An example of importing the whole library:

import mu from 'mu';

mu.app.get('/', function( req, res ) {
  res.send('Hello using full import');
} );

Dependencies

You can install additional dependencies by including a package.json file next to your app.js. It works as you would expect: just define the packages in the dependencies section of the package.json. They will be installed automatically at build time.

Developing with the template

Livereload is enabled automatically when running in development mode. You can embed the template easily in a running mu.semte.ch stack by launching it in the docker-compose.yml with the correct links. If desired, the chrome inspecor can be attached during development, giving advanced javascript debugging features.

Live reload

When developing, you can use the template image, mount the volume with your sources in /app and add a link to the database. Set the NODE_ENV environment variable to development. The service will live-reload on changes. You'll need to restart the container when you define additional dependencies in your package.json.

docker run --link virtuoso:database \
       -v `pwd`:/app \
       -p 8888:80 \
       -e NODE_ENV=development \
       --name my-js-test \
       semtech/mu-javascript-template

Develop in mu.semte.ch stack

When developing inside an existing mu.semte.ch stack, it is easiest to set the development mode and mount the sources directly. This makes it easy to setup links to the database and the dispatcher.

Optionally, you can publish the microservice on a different port, so you can access it directly without the dispatcher. In the example below, port 8888 is used to access the service directly. We set the path to our sources directly, ensuring we can develop the microservice in its original place.

yourMicroserviceName:
  image: semtech/mu-javascript-template
  ports:
    - 8888:80
  environment:
    NODE_ENV: "development"
  links:
    - db:database
  volumes:
    - /absolute/path/to/your/sources/:/app/

Attach the Chrome debugger

When running in development mode, you can attach the chrome debugger to your microservice and add breakpoints as you're used to. The chrome debugger requires port 9229 to be forwarded, and your service to run in development mode. After launching your service, open Google Chrome or Chromium, and visit chrome://inspect/.

Running through docker run, you could access the service as follows:

docker run --link virtuoso:database \
       -v `pwd`:/app \
       -p 8888:80 \
       -p 9229:9229 \
       -e NODE_ENV=development \
       --name my-js-test \
       semtech/mu-javascript-template

Now open Chromium, and visit chrome://inspect/. Once the service is launched, a remote target on localhost should pop up.

When running inside a mu.semte.ch stack, you could mount your sources and connect to known microservices as follows:

yourMicroserviceName:
  image: semtech/mu-javascript-template
  ports:
    - 8888:80
    - 9229:9229
  environment:
    NODE_ENV: "development"
  links:
    - db:database
  volumes:
    - /absolute/path/to/your/sources/:/app/

Now open Chromium, and visit chrome://inspect/. Once the service is launched, a remote target on localhost should pop up.