In this article, we explain what Cross-Origin Resource Sharing (CORS) is and how to avoid errors associated with it and the Access-Control-Allow-Origin header. This includes describing it both from the viewpoint of the frontend and the backend. CORS: Cross-Origin Resource Sharing Cross-Origin Resource Sharing (CORS) is a mechanism allowing (or disallowing) the resources to be […]
Nowadays, JavaScript is often used to make Ajax requests. There are a lot of libraries that can do that for us, for example, axios or jQuery. Both of them use XMLHttpRequest (XHR). It differs from the relatively new Fetch API that was introduced a few years ago. This article explains both of them and points out their […]
In this article, we cover ways to join strings. Even though it includes old methods of concatenating strings, we focus on template literals. Here you can learn how they work and how to expand their functionality with tags. Let’s go! Before template literals Back in the days, we didn’t have template literals and to merge […]
The array is a popular concept across many programming languages. At first glance, arrays work in the same way, but the JavaScript array differs from languages like C++. The article explains the basics of how JavaScript arrays work under the hood. It includes what are indexes and what is a maximum size of an array. Aside […]
IndexedDB is another API meant for client-side storage. It is good for storing a significant amount of data, including files. IndexedDB is more suitable than WebStorage for keeping structured data, and definitely more adequate for that than cookies. In this article, we go through the main concepts of IndexedDB. Basic concepts of IndexedDB IndexedDB is object-oriented […]
With the properties of objects, you can set more than just their values. In this article, you can learn what is the property descriptor and what you can achieve with it. Among other things, you can use getters and setters and the article also explains their concepts. Property descriptor A descriptor is a structure that holds information […]
WebSocket is a protocol that makes two-way communication in real-time between the user and the server possible. A common use cases are chats and online multiplayer games. Today we cover implementing it both on frontend and backend. Let’s go! Explaining WebSockets WebSocket is a different protocol than HTTP. Despite that, to establish a connection, the client sends […]
A common thing is for our application to fetch some data from the API. A problem with it is that might fail for various reasons, such as the API being down. We want our tests to be reliable and independent and to ensure that we can mock some of our modules. Mocking For the purpose […]
Hello! In the previous part of the tutorial, we’ve covered the very basics of testing React components with Enzyme. Today we will dig a bit deeper and learn how to test props, how (and why) use the mount function and what are the snapshot tests. Let’s go! Testing props In the previous article, we’ve tested […]
At the previous part of the tutorial, we’ve briefly covered the basics of unit testing. This time we will go further and start testing React with the Enzyme library. Thanks to the that, your application will be more reliable and it will be easier to avoid regression. Even though we will be using Jest here, Enzyme also works […]
