17233b2a66
Added a Caveat sub-section, and covered the refs aren't passed through case with an example. There are still a couple of more caveats. And left a reference to forwarding refs docs.
71 lines
2.5 KiB
Markdown
71 lines
2.5 KiB
Markdown
---
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title: Higher-Order Components
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---
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## Higher-Order Components
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In React, a **Higher-Order Component** (HOC) is a function that takes a component and return a new component. Programmers use HOCs to achieve **component logic reuse**.
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If you've used Redux's `connect`, you've already worked with Higher-Order Components.
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The core idea is:
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```jsx
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const EnhancedComponent = enhance(WrappedComponent);
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```
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Where:
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* `enhance` is the Higher-Order Component;
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* `WrappedComponent` is the component you want to enhance; and
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* `EnhancedComponent` is the new component created.
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This could be the body of the `enhance` HOC:
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```jsx
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function enhance(WrappedComponent) {
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return class extends React.Component {
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render() {
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const extraProp = 'This is an injected prop!';
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return (
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<div className="Wrapper">
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<WrappedComponent
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{...this.props}
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extraProp={extraProp}
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/>
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</div>
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);
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}
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}
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}
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```
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In this case, `enhance` returns an **anonymous class** that extends `React.Component`. This new component is doing three simple things:
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* Rendering the `WrappedComponent` within a `div` element;
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* Passing its own props to the `WrappedComponent`; and
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* Injecting an extra prop to the `WrappedComponent`.
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### Caveats
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Higher-order components come with a few caveats that aren’t immediately obvious if you’re new to React.
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#### Refs Aren't Passed Through
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While the convention for higher-order components is to pass through all props to the wrapped component, this does not work for refs. That’s because `ref` is not really a prop — like `key`, it’s handled specially by React. If you add a ref to an element whose component is the result of a HOC, the ref refers to an instance of the outermost container component, not the wrapped component.
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The solution for this problem is to use the React.forwardRef API (introduced with React 16.3)
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```jsx
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function enhance(WrappedComponent) {
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const wrapper = React.createRef((props,ref) => {
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return(
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<div className="Wrapper">
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<WrappedComponent
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{...props}
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ref={ref}
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/>
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</div>
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)
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})
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}
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```
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HOCs are just a pattern that uses the power of React's compositional nature. **They add features to a component**. There are a lot more things you can do with them!
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## Other Resources
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* [React docs: Higher-Order Components](https://reactjs.org/docs/higher-order-components.html)
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* [React docs: Forwarding Refs](https://reactjs.org/docs/forwarding-refs.html)
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