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refactor: change defaultProps generation for react #1661

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@nmerget nmerget commented Jan 15, 2025

Description

Please provide the following information:

closes #1471

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@nmerget nmerget requested a review from samijaber as a code owner January 15, 2025 10:01
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🦋 Changeset detected

Latest commit: 95b5378

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@nmerget Thanks a lot for tackling this long overdue refactor!

There is however one big drawback to your approach: by writing props = { /* DEFAULT_PROPS */}, you are overwriting any props that do not have defaults!

See this example:

CleanShot 2025-01-15 at 08 03 11@2x

type Props = {
  foo?: string;
  bar?: string;
};

// BEFORE
const A = (props: Props) => <div>B: {JSON.stringify(props)}</div>;
A.defaultProps = { foo: 'bar' };

// AFTER
const B = (props: Props = { foo: 'bar' }) => (
  <div>A: {JSON.stringify(props)}</div>
);

// FIX
const C = (props: Props) => {
  props = { ...props, foo: 'bar' };
  return <div>C: {JSON.stringify(props)}</div>;
};

export default function App() {
  return (
    <>
      <A bar="another-prop" />
      <B bar="another-prop" />
      <C bar="another-prop" />
    </>
  );
}

I think we need to instead use the approach i provide in C

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nmerget commented Jan 16, 2025

const C = (props: Props) => {
  props = { ...props, foo: 'bar' };
  return <div>C: {JSON.stringify(props)}</div>;
};

This would always overwrite the given props with the default value, wouldn't it? :P

@nmerget nmerget requested a review from samijaber January 17, 2025 11:40
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const C = (props: Props) => {
  props = { ...props, foo: 'bar' };
  return <div>C: {JSON.stringify(props)}</div>;
};

This would always overwrite the given props with the default value, wouldn't it? :P

Woops, you're right. I should have written:

const C = (props: Props) => {
  props = { foo: 'bar', ...props };
  return <div>C: {JSON.stringify(props)}</div>;
};

To re-illustrate my point, here's an updated example:

CleanShot 2025-01-17 at 11 28 33@2x

As you can see, <B /> never sets the default-value in any situation.

Essentially, const MyComp = (props = DEFAULT_VALUES) => {} will never do anything because the props object will always exist. DEFAULT_VALUES will only be used if props is undefined, which is never the case (at worst it's an empty object).

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React's defaultProps will be remove from function components in a future release
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