GraphQL Apollo Starter Kit (Lerna, Node.js)

In many ways developing in Node.js is very fast and lightweight. However it can also be bewildering at times. Mostly so since for everything there seems to be more than one established way of doing things. Moreover, the right way to do something can change within 3 to 6 months, so best practices documented in books and blogs quickly become obsolete.

Some days ago I wanted to create a simple sample project that shows how to develop a simple client/server application using Apollo and React. I thought this would be a simple undertaking. I imagined I would begin with a simple tutorial or ‘starter kit’ and quickly be up and running.

I found that things were not as easy as I imagined, since there are plenty of examples to spin up a simple react app chiefly using create-react-app. I also found the awesome apollo-universal-starter-kit. However, the former lacks insight of how to link this to a Node.js back-end server and the latter is a bit complex and opinionated in some ways as to which frameworks to use.

This motivated me to develop a small, simple ‘starter kit’ for Apollo Client and Server in GraphQL with the following features:

  • Uses ES 2018 ‘vanilla’ JavaScript
  • Uses Lerna to define project with two packages (client and server)
  • Uses Node.js / Express as web server
  • Uses Babel to allow using ES 6 style modules for Node.js
  • Provides easy ways to start a development server and spin up a production instance

Here a link to the project on GitHub:

graphql-apollo-starter-kit

The README provides the instructions to run and build the project.

A few things of note about the implementation:

This project is aimed at developers new to Node.js/React/Apollo. It is not implemented in the most elegant way possible but in a way which makes it easy to understand what is going on by browsing through the code. Be welcome to check out the project and modify it!

Mastering Modular JavaScript

Today I was having a look around for best practices for defining JavaScript modules. In that search, I came across the book Mastering Modular JavaScript. This book offers a good selection of best practices for JS module development. Also, all chapters are freely available on GitHub:

For a more basic introduction to modules, see the chapter JavaScript Modules from the book Practical Modern JavaScript.

Everything new in JavaScript since ES6

It is no secret that things in the tech world change rather rapidly. It’s difficult to keep track of everything at the same time. For instance I have been working with JavaScript quite extensively some years ago but recently have been more involved with other tech stacks. Thus I have only followed the developments in the JavaScript world sporadically and was quite surprised by how many things have changed since the days of JavaScript: The Good Parts.

Since before ES6 things have not changed much for a long time, I imagine I am not the only one who could benefit from a little refresher of all the things that have changed since ES6. Thus I have compiled some of the changes I think are most important for ordinary development work. The idea is to provide a quick overview rather than explain every feature in detail – assuming that more information on any of the changes is readily available on the web.

This is not a complete list of everything that has changed. For instance, I included promises but omitted changes made to the way regular expressions work in ECMAScript 2018; since we are likely to come across promises many times per day whereas the changes to regular expressions only affect us in particular edge cases.

ECMAScript 6 / ECMAScript 2015

Variable Scoping

  • let x = 1;: To define block scoped variables

Arrow Functions

  • x => x + 1: Concise closure syntax
  • x => { return x + 1; }: Concise closure syntax
  • this: within lambdas refers to enclosing object (rather than to lambda function itself)

Promises

Promises for wrapping asynchronous code.


let p = new Promise((resolve, reject) => {

   resolve("hello");

});

p.then((msg) => console.log(msg)); 

Executing asynchronous operations in parallel

let parallelOperation = Promise.all([p1, p2]);
parallelOperation.then((data) => {let [res1, res2] = data; } );

Default Parameters and Spread Operator

  • function (x = 1, y = 2): Default values for function parameters
  • function (x, y, ...arr) {}: Capturing all remaining arguments in array for variadic functions
  • var newarr = [ 1, 2, ...oldarr]: ‘Spreading’ of elements from an array as literal elements
  • multiply(1, 2, ...arr): Spreading of elements from an array as individual function parameters

Multiline Strings and Templates

  • `My String⏎NewLine`: Multi-line string literals
  • `Hello ${person.name}`: Intuitive string interpolation
  • const proc = sh`kill -9 ${pid}`;: Tagged template literals for parsing custom languages. The example would result in calling the function sh with the parameters (['kill -9 '], pid)

Object Properties

  • let obj = { x, y }: Property shorthand for defining let object = { x: x, y: y }
  • obj = { func1 (x, y) { } }: Methods allowed as object properties

Deconstructor Assignment

  • var [ x, y, z ] = list: Deconstructing arrays into individual variables by assignment.
  • var [ x=0, y=0 ]: Default values for deconstructing arrays.
  • function( [ x, y ] ): Deconstructing arrays in function calls.
  • var { x, y, z } = getPoint(): Deconstructing objects into individual variables by assignment.
  • var { name: name, address: { street: street }, age: age} = getData(): Deconstructing objects into individual variables by assignment, including nested properties.
  • var p = { x=0, y=0 }: Default values for deconstructing objects.
  • function( { x, y } ): Deconstructing objects in function calls.

Modularity

  • export function add(x,y) { return x + y; }: Exporting functions
  • export var universe = 42;: Exporting variables
  • import { add, universe } from 'lib/module';: Importing functions and variables
  • import * from 'lib/module': Wildcard import
  • export default (x, y) => x + y;: Defining default export
  • import add from 'lib/add': Importing default export
  • import add, { universe } from 'lib/add': Importing default export and additional exports
  • export * from 'lib/module';: Reexporting from other modules

Classes

class keyword for constructing simple classes.

class Point {

  constructor (x, y) {
     this.x = x;
     this.y = y;
  }

  move (deltax, deltay) {
     new Point(this.x + deltax, this.y + deltay);
  }

}

extends keyword for extending classes:


class Car extends Vehicle {

  constructor (name) {
     super(name);
  }

static keyword for static methods


class Math {

  static add(x, y) {
    return x + y;
  }

}

get and set keywords for decorated property access.


class Rectangle {

  get area() { return this.x * this.y }

}

...

new Rectangle(2, 2).area === 4;

Iteration Through Object Values

  • for (let value of arr) { }: for … of loop for going iterating through values of objects.
  • Also note that objects can define their own iterators and generators

Data Structures

  • new Set(): For sets
  • new Map(): For maps
  • new WeakSet(): For sets whose items will be garbage collected when required
  • new WeakMap(): For sets whose items will be garbage collected when required

Symbols

  • Symbol(): For creating an object with a unique identity.
  • Symbol("note"): For creating a unique object with a descriptor.
  • Note: Symbol("node") !== Symbol("node")

ECMAScript 2016

  • **: Exponentiation operator
  • Array.prototypes.includes: Like indexOf but with true/false result and support for NaN

ECMAScript 2017

async/await for more expressive asynchronous operations

async function add1(x) {
  return x + 1;
}

async function add2(x) {
  let y = await add1(x);
  return await add1(y);
}

add2(5).then(console.log);

ECMAScript 2018

Rest/Spread Operators for Object Properties

Collect all not deconstructed properties from an object in another object:


var person = { firstName: "Paul", lastName: "Hendricks", password: "secret"};
var {password, ...sanitisedPerson } = person;
// sanitisedPerson = {firstName: "Paul", lastName: "Hendricks"}

Spread object properties

let details = { firstName: "Paul", lastName: "Hendricks" };

let user = { ...details, password: "secret" };

Finally for Promises

finally callback is guaranteed to be executed if promise succeeds or fails.


async function sayHello() {
console.log("hello");
}
sayHello().then(() => console.log("success") )
.catch((e) => console.log(e))
.finally(() => console.log("runs always")

for await Loop

Special for loops that resolve promises before every iteration.


const promises = [
  new Promise(resolve => resolve(1) ),
  new Promise(resolve => resolve(2) )
];

async function runAll() {
  for await (p of promises) {
    console.log(p);
  }
}

runAll();

References

Image credits: Flickr

Test if Firebase is Initialized on Node.JS / Lambda

Firebase is build on the assumption that it will only be initialized once.

This can be a problem in Node.JS applications sometimes, especially if they are run as part of an Amazon Lambda function.

This can lead to errors as the following:

Firebase App named '[DEFAULT]' already exists.

Thankfully, there is an easy way to check if Firebase has already been initialized (firebase.initializeApp). Just wrap your call to initializeApp in the following:

if (firebase.apps.length === 0) {
    firebase.initializeApp({
        serviceAccount: {
            ...
        },
        databaseURL: ...
    });
}

Sources

Sandboxing JavaScript in Java App – Link Collection

The JVM is by design an insecure environment and it is generally difficult to run untrusted code in a sandboxed environment.

However, it seems that is relatively easy to sandbox JavaScript code running in Oracle Nashorn. The instructions are here. Strangely, this was not easy to find through a Google search.

Below I have listed some further sources on Sandboxing JavaScript and Java code. Although there is plenty of material on Rhino, I would not recommend using this engine. I think Nashorn has been designed with support for Sandboxed code in mind from the very beginning while in Rhino the functionality feels kind of bolted on.

UPDATE I have implemented two little libraries which takes care of the grunt work of sandboxing Nashorn and Rhino code in Java:

Nashorn Sandbox (on GitHub)

Rhino Sandbox (on Github)

Sandboxing JavaScript

Nashorn

Restricting Script Access to Specified Java Classes: From the Oracle Nashorn docs. Shows how to restrict access to specific Java classes.

Rhino

Class ContextFactory: Useful for monitoring and setting restrictions on Rhino code.

Method initSafeStandardObjects: Useful for creating sandboxed Rhino code.

Rhino Sandbox: A small library for sandboxing JavaScript code running in Rhino.

Sandboxing Rhino in Java: Blog post

Securing Rhino in Java6: Blog post

DynJS

Sandboxing JavaScript Execution in Java: Blog post

Sandboxing Java

Example Code Monitoring Threads: Example code how thread CPU usage can be monitored.

The Java Sandbox: A library for sandboxing any Java code. Might be useful to sandbox the Java code with runs the script.

Fix Firefox ‘Permission denied to access property document’

Problem

You are trying to load a script from a local file into a page displayed in Firefox (as can sometimes be useful for testing).

Firefox reports an error such as

Error: Permission denied to access property ‘document’

Error: Permission denied to access property ‘local’

Solution

This problem is caused by a security restriction that should normally be in place. However, you can temporarily disable this security feature as follows:

  • Enter the address ‘about:config’ in your Firefox
  • Search for ‘strict_’
  • Double click on the value column for the preference ‘security.fileuri.strict_origin_policy‘ to switch it from ‘true’ to ‘false’.

Remember to reenable the policy once your tests are done!

Sources

https://bugzilla.mozilla.org/show_bug.cgi?id=477201

https://support.mozilla.org/en-US/questions/1003768

CodeMirror 3 Indent All Lines / Autoformat

Problem

You have created an instance of a CodeMirror and initialized it with some text and would like to correct its indentation or you would like to give the user the option to ‘autoformat’ the text entered.

Solution

Iterate over all lines in the editor and indent them individually:

var e = CodeMirror.fromTextArea(textarea.get(0), {});

for (var i=0;i<e.lineCount();i++) { e.indentLine(i); }

This should indent all lines in your editor nicely:

Note that in CodeMirror 2 there was an autoformatter add-in which is not officially supported for CodeMirror 3.

Remove Duplicates from Array in CoffeeScript

Problem

You have an array in CoffeeScript, which contains equal elements multiple times such as:

[1,1,2,3,3]

You would like to have only unique values in the array. Thus, transform it into:

[1,2,3]

Solution

You can use the following method to accomplish such:

removeDuplicates = (ar) ->
  if ar.length == 0
    return []  
  res = {}
  res[ar[key]] = ar[key] for key in [0..ar.length-1]
  value for key, value of res

alert(removeDuplicates([1,2,3,3,4,4,5]));

References

This solution is based on this approach (with a few minor issues fixed).

Insert Text at Caret Position in Summernote Editor for Bootstrap

Problem

Using the very useful Summernote Editor component for Bootstrap, you would like to insert some text at the current caret position programmatically.

Solution

The Summernote API does not provide any dedicated methods for inserting text. However, that’s not a problem since we can use the JQuery/native DOM API to insert text into the editor. Thankfully, the content of the Summernote editor is nothing but vanilla HTML/DOM elements. Thus, we can insert text at the current cursor position as follows (if the Summernote editor is focused):

To Insert at the End of the Current Paragraph

$(document.getSelection().anchorNode.parentNode).append(“appended!”);

To Insert at the Current Cursor Position

var selection = document.getSelection();
var cursorPos = selection.anchorOffset;
var oldContent = selection.anchorNode.nodeValue;
var toInsert = "InsertMe!";
var newContent = oldContent.substring(0, cursorPos) + toInsert + oldContent.substring(cursorPos);
selection.anchorNode.nodeValue = newContent;

Note: You probably will have to work some magic with the document.getSelection() call. The problem is that once you would click a button or trigger the action in some other way, the selection would change. Thus, I save a reference to the document.getSelection() upon every focus and key press event on the editor.

Insert at Current Position (Alternative)

As suggested by Dexter in the comments below, you can also insert text as follows:

$(‘#summernote’).summernote('editor.saveRange');

// Editor loses selected range (e.g after blur)

$(‘#summernote’).summernote('editor.restoreRange');
$(‘#summernote’).summernote('editor.focus');
$(‘#summernote’).summernote('editor.insertText', 'This text should appear at the cursor');

References

MDN – Selection.anchorNode

Stackoverflow – Get caret position in contentEditable div

Stackoverflow – Inserting Text at Cursor Position using JS/JQuery

Stackoverflow – JQuery Plugin for Inserting Text at Caret

CoffeeScript Fat Arrow (=>) explained

Anyone who has worked with JavaScript for anything but a very short time will have come across the problem that the meaning of ‘this’ is often ambiguous at best. CoffeeScript attempts to mitigate this problem somewhat by introducing the Fat Arrow operator (=>). This operator can be used as a replacement for the thin arrow operator (->) used extensively in CoffeeScript for defining functions.

Unfortunately, it is not easy to understand what the fat arrow operator does.I hope the following rules provide some guidance on how to use this operator in CoffeeScript:

Rule 1: You Don’t Need the Fat Arrow If You Don’t Use: class, this, and @

If you are a beginner in JavaScript and/or CoffeeScript, I would recommend keeping your hands of the language constructs ‘this’, ‘class’ and ‘@’. You can implement any application you like without having to use these constructs and it will make your applications more robust and bug free.

Rule 2: Use the Fat Arrow when You Use @ in a Callback Definition in a Method

If you use classes in your code and you want to create a new anonymous function to be passed as a callback (such as to listen to an onclick event or to defined setTimeout function), define this function with the fat arrow operator. This will assure that you still have access to the methods and properties of the class you are working with.

The fat arrow will ‘override’ the default meaning of the @ operator as follows, to assure that ‘this’ refers to what we would expect it:

CoffeeScript

delayedAction = =>  
  alert(@messsage)

setTimeout(delayedAction, 100);

JavaScript

delayedAction = (function(_this) {
  return function() {
    return alert(_this.messsage);
  };
})(this);

setTimeout(delayedAction, 100);

Rule 3: Don’t Use Methods as Callbacks and Avoid the Fat Arrow Operator in All Other Circumstances

There is one more use case for the Fat Arrow operator, which is that it has a special meaning when used for the definition of class methods. This is useful when the methods of a class are to be passed as a callback. I personally don’t think that’s a very useful feature and it’s better to define an anonymous function to handle a callback and then call a method of your class/object from within this callback. Following this rule enables us not having to worry about whether to define a method with a thin or fat arrow – which is otherwise tricky since the right choice here is external to the class we are writing.

More Reading

Karl Seguin – Ten Features I Like About CoffeeScript

Michael Kramer – The Simplified Fat Arrow Guide for CoffeeScript

Azat Mardanov – Understanding Fat Arrows (=>) in CoffeeScript

Giang Nguyen – Coffeescript: Fat arrow vs thin arrow