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React Compiler compatibility module for codebases unable to use React 19
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module.exports = function(api) { | |
return { | |
plugins: [ | |
[ | |
'babel-plugin-react-compiler', { | |
runtimeModule: 'react-compiler-runtime' | |
} | |
] | |
] | |
} | |
} |
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{ | |
"dependencies": { | |
"react-compiler-runtime": "file:./lib/react-compiler-runtime" | |
}, | |
"devDependencies": { | |
"babel-plugin-react-compiler": "latest" | |
} | |
} |
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// lib/react-compiler-runtime/index.js | |
const React = require('react'); | |
const $empty = Symbol.for("react.memo_cache_sentinel"); | |
/** | |
* DANGER: this hook is NEVER meant to be called directly! | |
* | |
* Note that this is a temporary userspace implementation of this function | |
* from React 19. It is not as efficient and may invalidate more frequently | |
* than the official API. Please upgrade to React 19 as soon as you can. | |
**/ | |
export function c(size: number) { | |
return React.useState(() => { | |
const $ = new Array(size); | |
for (let ii = 0; ii < size; ii++) { | |
$[ii] = $empty; | |
} | |
// @ts-ignore | |
$[$empty] = true; | |
return $; | |
})[0]; | |
} |
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// lib/react-compiler-runtime/package.json | |
{ | |
"name": "react-compiler-runtime", | |
"version": "0.0.1", | |
"license": "MIT", | |
"main": "index.js", | |
"dependencies": { | |
"react": "^18.2.0" | |
} | |
} |
I'm curious, why does the polyfill appear to return the first element of the created array instead of the array itself? surely that is a mistake?
@jaeschliman With the react function useState
, it returns a tuple containing 2 values. The first one is the state, the second one is a setter for the state. We are only interested in the state from the useState
and discard the setter. Note that it is rare to not use the setter, most of the time when you use useState
, you actually want to be able to change the state, not just here
More reading of the useState
hook: https://react.dev/reference/react/useState
@ferrybig ah yes, of course — I am so used to seeing it written with the destructuring syntax that I was blind to that — thanks
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@poteto I'm curious, why does the polyfill appear to return the first element of the created array instead of the array itself? surely that is a mistake?