It may seem plausible for a for-of loop to iterate through lines in a file but ultimately it can’t execute until it has received the whole contents.
For an object to become an iterator it needs to know how to access values in a collection and to keep track of its position in the list. This is achieved by an object implementing a next method and returning the next value in the sequence. This method should return an object containing two properties: value and done. It must have the [Symbol.iterator] as well, as this is key to using the for..of loop.
This post has lots of code examples showing promises, async/await and unit testing async functions. There is a coding challenge at the end to test your learning.
What do promises solve in our code?
Whenever you wanted to resolve some data asynchronously it had to be done via a callback. In complex applications this led to “callback hell”, when the first data fetch was resolved another data fetch needs to happen afterwards. This would repeat a few times, creating a “nice” sideways pyramid in your code.
Promises mostly solved that problem by chaining. Each step resolved data and passed it along to the next then function.
In this post, I will discuss the why and how to use React JS Render Props.
Why use Render Props: Promote reuse of behaviour across React components.
If you have read my post on higher-order components this may seem similar. The React community has been working hard on solving reuse across components, and one common theme is passing data to children. However, we will focus here on how to use Render Props - and discuss the differences between HOC and Render Props in another post.
Have you ever written a unit test and it seems to take a long time to make green?
What is a long time, you might ask? In my opinion if you spend more than 5 minutes solving the test you wrote then you are in the amber zone that you made it too complex. If greater than 10 minutes then you need to simplify the test. Which might not seem like an obvious thing to do.
This exercise is to help unblock the solving of complex tests consistently and quicker.
In this post I will discuss why and how to use higher-order components (HOC) with React JS.
Why use HOC: Promote reuse of logic across React components.
Components are the typical element for reuse in React but sometimes features don’t fit into this standard. There might be similar methods used to fetch data but maybe the display is different. An example of this is shown later.
As with any new tech it can be overwhelming and confusing how all the parts work together. Especially with the combo of Relay and GraphQL. Hopefully this post will help demystify some things in Relay.
Why use it: One typical issue found in an SPA are the number of network calls made to render a page. Quickly this starts to affect your server performance because the requests made can be high. Relay is focused around efficient network calls helping to mitigate this issue. Another good feature is the queries are close to the components making it obvious the data requirements.