Podcast
Questions and Answers
What is one of the characteristics of a pure function?
What is one of the characteristics of a pure function?
- It minds its own business (correct)
- It changes variables that existed before it was called
- It returns different results for the same inputs
- It is only used in object-oriented programming
What is the benefit of writing components as pure functions?
What is the benefit of writing components as pure functions?
- It is only used in functional programming
- It makes the code more complex
- It avoids an entire class of baffling bugs and unpredictable behavior (correct)
- It only works in small codebases
What is an example of a pure function?
What is an example of a pure function?
- A function that returns different results for the same inputs
- A function that is only used in object-oriented programming
- The double function in JavaScript (correct)
- A function that changes variables that existed before it was called
What does React assume about the components you write?
What does React assume about the components you write?
What does a pure function always return given the same inputs?
What does a pure function always return given the same inputs?
What is a benefit of using Strict Mode?
What is a benefit of using Strict Mode?
What is a way to keep components pure?
What is a way to keep components pure?
What can be thought of as recipes?
What can be thought of as recipes?
Why does React care about purity in components?
Why does React care about purity in components?
What should you do if you can't find the right event handler for your side effect?
What should you do if you can't find the right event handler for your side effect?
What is a characteristic of a pure function in React?
What is a characteristic of a pure function in React?
Why is it safe to stop calculating at any time in React?
Why is it safe to stop calculating at any time in React?
What should you do to update the screen in React?
What should you do to update the screen in React?
What is a benefit of writing pure functions in React?
What is a benefit of writing pure functions in React?
Why should you strive to express your component's logic in the JSX you return?
Why should you strive to express your component's logic in the JSX you return?
What should you do when you need to 'change things' in React?
What should you do when you need to 'change things' in React?
What does the component serve to React to render?
What does the component serve to React to render?
What is the issue with calling the component multiple times?
What is the issue with calling the component multiple times?
What makes a component 'pure'?
What makes a component 'pure'?
What is the purpose of StrictMode in React?
What is the purpose of StrictMode in React?
What is the issue with the original component example?
What is the issue with the original component example?
What is local mutation in React?
What is local mutation in React?
Where do side effects usually belong in React?
Where do side effects usually belong in React?
What is the result of calling a pure function twice?
What is the result of calling a pure function twice?
What is the issue with changing preexisting variables or objects while rendering?
What is the issue with changing preexisting variables or objects while rendering?
What is the purpose of treating inputs as read-only in React?
What is the purpose of treating inputs as read-only in React?
Study Notes
Pure Functions in React
- A pure function has three characteristics:
- It minds its own business (does not change external variables or objects)
- Same inputs, same output
- Given the same inputs, the function always returns the same result
- Writing pure functions in React helps avoid bugs and unpredictable behavior
- React components should be written as pure functions, which means:
- They only perform calculations and do not change external variables or objects
- Same inputs, same JSX output
- Given the same inputs, the component always returns the same JSX
Benefits of Pure Functions
- Allow components to be rendered in any order
- Enable caching and skipping re-renders when inputs haven't changed
- Allow React to safely stop calculating at any time
- Enable server-side rendering
- Unlock the power of the React paradigm for features like data fetching, animations, and performance
Detecting Impure Functions with Strict Mode
- Strict Mode calls each component's function twice during development to detect impure functions
- Impure functions can cause confusing bugs and unpredictable behavior
- Pure functions are not affected by Strict Mode and will always return the same result
Local Mutation vs. External Mutation
- Local mutation: changing variables or objects created within the component's scope
- External mutation: changing variables or objects created outside the component's scope
- Pure functions do not mutate external variables or objects
Side Effects and Event Handlers
- Side effects: changes that occur outside of rendering, e.g. updating the screen, starting an animation, changing data
- Event handlers: functions that React runs in response to user actions, e.g. clicking a button
- Event handlers do not need to be pure functions and can cause side effects
useEffectcan be used as a last resort to attach side effects to the returned JSX
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Description
Learn about the benefits of using pure functions in JavaScript, how to keep components pure, and how to use Strict Mode to find mistakes.
