devBlog of Michal Zalecki

Writing clean code with memoized event handlers

When we talk about writing asynchronous JavaScript we often use timer functions or promises as an example. Whereas the majority of asynchronous code written in modern JavaScript web apps is focused on events caused either by a user interacting with the UI (addEventListener) or some native API (IndexedDB, WebSocket, ServiceWorker). With modern front-end frameworks and the way we pass event handlers it is easy to end up with leaky abstraction.

Optimize React build for production with webpack

This guide is a form of writing down few techniques that I have been using with ups and downs for the past two years. Optimizations highly depend on your goals, how users are experiencing your app, whether you care more about time to interactive or overall size. It should not come as a surprise, that like always, there is no silver bullet. Consider yourself warned. Although you have to optimize for your use cases, there is a set of common methods and rules to follow. Those rules are a great starting point to make your build lighter and faster.

Converting DOCX to PDF using Python

When you ask someone to send you a contract or a report there is a high probability that you’ll get a DOCX file. Whether you like it not, it makes sense considering that 1.2 billion people use Microsoft Office although a definition of “use” is quite vague in this case. DOCX is a binary file which is, unlike XLSX, not famous for being easy to integrate into your application. PDF is much easier when you care more about how a document is displayed than its abilities for further modifications. Let’s focus on that.

Implementing Geofencing with HERE

Geofencing allows for locating points within defined geographic areas. Areas can be defined with geographic points, consisting of latitude and longitude, forming any shape. HERE provides Geofencing Extension API for that purpose.

The Best React Boilerplate: DIY

I know, I know. This title sounds cocky. In fact, it makes a lot of sense if you think about it. I’ve been asked multiple times by my friends from our local React meetup group I’m organizing or by teams I’m helping to develop their applications for a starter, boilerplate or a setup. This post is a result of another such question. Most of the time it’s one of the two scenarios.

Why using localStorage directly is a bad idea

If you are working on web services for some time you probably remember, or at least heard about, The First Browser War. We are extremely lucky that this scramble between Internet Explorer and Netscape turned into a great race for better, faster, more unified web experience. That said, we’re still facing a lot of inconsistency or not trivial edge cases while working with so-called browser APIs.

React components and class properties

React components went the long way from React.createClass through ES2015 powered React.Component to React.PureComponent and stateless functional components. I really enjoy the idea that we don’t have to “hack” the language anymore, at least not that much as we used to. The progress in this department is quite clear and brings not always obvious benefits. Using constructs built into the language/transpiler instead of relying on framework’s factory functions or constructors accepting huge configuration objects future proofs your code.

Custom root domain and SSL on Heroku

Heroku managed to significantly lower the bar when it comes to deploying applications and integrating them with third-parties through various add-ons. It can be argued, but in my opinion optimizing platform to be easy at the entry-level made it much harder to do some more advanced setups. It’s strange but for quite a long time of using Heroku and feeling comfortable with it I’ve never had to configure it from A to Z. I was treating Heroku as some kind of rapid prototyping environment and finally migrating it to more dedicated solutions. That said, for one of the projects Heroku turned out to be a great fit and it made sense to keep it that way. So, now I only have to set up a root domain.

Why I use double quotes in JavaScript

Coding style is often a topic of fierce debates, mostly unnecessary. What matters is being consistent throughout the project, or better, your entire codebase. Tools like JSHint, JSCS and ESLint contribute and popularized advantages which come from keeping code style consistent. I’m used to airbnb/javascript style guide with couple exceptions and this post justify my decision to go for double quotes in our entire JavaScript codebase.

Set up Selenium for Firefox and Chrome

Automated browser tests, in my case, are often part of continuous integration (CI). Failure = no deploy. This naturally creates some expectations towards acceptance/end to end testing framework. I haven’t found the tool which would meet all requirements although CodeceptJS is close. Nevertheless, no matter whether you use Protractor, Nightwatch.js, WebdriverIO, CodeceptJS or anything else based on Selenium you need to set it up and make it talk to the browser.

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