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* Update CHANGELOG Changelog run: https://github.com/yewstack/yew/actions/runs/6283917852/job/17064800916 * docusaurus docs:version 0.21 * migration guide * blog post * prettier * make website warnings go away * make GA work * Apply suggestions from code review * Apply suggestion from review Co-authored-by: Kaede Hoshikawa <futursolo@users.noreply.github.com> * prettier --------- Co-authored-by: Kaede Hoshikawa <futursolo@users.noreply.github.com>
40 lines
1.3 KiB
Plaintext
40 lines
1.3 KiB
Plaintext
---
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title: 'Pure Components'
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---
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A function component is considered [pure] when the returned `Html` is deterministically derived
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from its props when its view function does not mutate its state or has other side effects.
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[pure]: https://en.wikipedia.org/wiki/Pure_function
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The example below is a pure component. For a given prop `is_loading` it will always result in the same `Html` without any side effects.
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```rust
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use yew::{Properties, function_component, Html, html};
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#[derive(Properties, PartialEq)]
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pub struct Props {
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pub is_loading: bool,
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}
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#[function_component]
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fn HelloWorld(props: &Props) -> Html {
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if props.is_loading {
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html! { "Loading" }
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} else {
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html! { "Hello world" }
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}
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}
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```
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:::note
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If you have an internal pure component that makes no use of hooks and other component machinery, you can often write it instead
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as a normal function returning `Html` and avoid a bit of overhead for Yew, related to running the component lifecycle. Use
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[expression syntax](concepts/html/literals-and-expressions.mdx#expressions) to render them in `html!`.
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:::
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## Impure components
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You might wonder if a component can be impure if it does not use any globals, since it is just a function that is called every render.
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This is where the next topic comes in - [hooks](./hooks)
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