![]() #4: useEffect handler ran the first time after the mount - DOM element already had the default state (‘AAPL’). #1, 2, 3: Upon mounting, Component is rendered with default ticker (‘AAPL’). Let’s look at the execution log closely to understand what’s happening. The execution log is a result of three actions: const onChange = event => ) īelow is the simplified code (full version is here). Here is the relevant portion of the component (full code here). ![]() The active ticker which is shown on the UI is stored in a local state using useState hook. We will implement the Ticker component as per the above sketch. Let’s understand the workings of useState with an example. UseState hook is the primary building block which enables functional components to hold state between re-renders. The dropdown allows users to pick a different ticker. This component shows a ticker symbol and its price. We will implement a simple stock ticker component and add functionality around this component to understand the behavior of various built-in hooks.* Parent component re-renders due to any of the above reasons.Įvery mention of ‘re-render’ in this post is about the “render phase” mentioned above. * Context value is updated (if the component listens to context change using useContext). Now, what prompts React to trigger the render phase? This StackOverflow’s post provides a succinct answer. * The “render” phase: create React elements React.createElement ( learn more) * The “reconciliation” phase: compare previous elements with the new ones ( learn more) * The “commit” phase: update the DOM (if needed). Table of ContentsĪt a high level, React goes through three phases whenever it converts the component tree and flushes the result to the rendering environment: If you are interested in only a specific hook, please go directly from the links below. This is a long post covering most of the built-in hooks with lot of screenshots and examples. I’ll share my learnings with detailed examples and also highlight some pitfalls I ran into. This post is a result of my explorations to understand how each built-in hook influences the component re-renders/lifecycle. While this non-explicit nature allows extracting re-usable behavior into custom hooks with much less boilerplate code, what I found myself lacking was the clear understanding of how hooks impact the execution flow. Sometimes I couldn’t explain why my component gets re-rendered ( seems like a common question), what change caused an infinite re-render loop ( another common one) and other times I wasn’t sure whether my usage of useCallback/useMemo is actually improving the performance.įunctional components using hooks will go through a lifecycle but without explicit lifecycle methods unlike their class based counterparts. But once I started using them, I felt a gap in my understanding around the component lifecycle. ![]() When I started working on React Hooks, the official documentation explained the core concepts quite well - motivation behind hooks, detailed api reference, rules of hooks, answering several frequently asked questions.
0 Comments
Leave a Reply.AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |