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Lazy components must use React.lazy #13885

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@acdlite
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@acdlite acdlite commented Oct 19, 2018

Note: This proposal has been discussed in reactjs/rfcs#64.

Removes support in master for using arbitrary promises as the type of a React element. Instead, promises must be wrapped in React.lazy. This gives us flexibility later if we need to change the protocol.

The reason is that promises do not provide a way to call their constructor multiple times. For example:

const promiseForA = new Promise(resolve => {
  fetchA(a => resolve(a));
});

Given a reference to promiseForA, there's no way to call fetchA again. Calling then on the promise doesn't run the constructor again; it only attaches another listener.

In the future we will likely introduce an API like React.eager that is similar to lazy but eagerly calls the constructor. That gives us the ability to call the constructor multiple times. E.g. to increase the priority, or to retry if the first operation failed.

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@sizebot sizebot commented Oct 19, 2018

Details of bundled changes.

Comparing: 0648ca6...173ed32

scheduler

File Filesize Diff Gzip Diff Prev Size Current Size Prev Gzip Current Gzip ENV
scheduler.development.js n/a n/a 0 B 19.17 KB 0 B 5.74 KB UMD_DEV
scheduler.production.min.js n/a n/a 0 B 3.16 KB 0 B 1.53 KB UMD_PROD

Generated by 🚫 dangerJS

@acdlite acdlite force-pushed the acdlite:lazy-components-must-use-react-lazy branch from 83f226a to 738f23f Oct 19, 2018
@acdlite acdlite force-pushed the acdlite:lazy-components-must-use-react-lazy branch from 738f23f to 270fb63 Oct 19, 2018
Removes support for using arbitrary promises as the type of a React
element. Instead, promises must be wrapped in React.lazy. This gives us
flexibility later if we need to change the protocol.

The reason is that promises do not provide a way to call their
constructor multiple times. For example:

const promiseForA = new Promise(resolve => {
  fetchA(a => resolve(a));
});

Given a reference to `promiseForA`, there's no way to call `fetchA`
again. Calling `then` on the promise doesn't run the constructor again;
it only attaches another listener.

In the future we will likely introduce an API like `React.eager` that
is similar to `lazy` but eagerly calls the constructor. That gives us
the ability to call the constructor multiple times. E.g. to increase
the priority, or to retry if the first operation failed.
@acdlite acdlite force-pushed the acdlite:lazy-components-must-use-react-lazy branch from 270fb63 to 22cdad1 Oct 19, 2018
@acdlite acdlite force-pushed the acdlite:lazy-components-must-use-react-lazy branch 2 times, most recently from 6298bb4 to 173ed32 Oct 19, 2018
@acdlite acdlite merged commit d9659e4 into facebook:master Oct 19, 2018
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linjiajian999 pushed a commit to linjiajian999/react that referenced this pull request Oct 22, 2018
Removes support for using arbitrary promises as the type of a React
element. Instead, promises must be wrapped in React.lazy. This gives us
flexibility later if we need to change the protocol.

The reason is that promises do not provide a way to call their
constructor multiple times. For example:

const promiseForA = new Promise(resolve => {
  fetchA(a => resolve(a));
});

Given a reference to `promiseForA`, there's no way to call `fetchA`
again. Calling `then` on the promise doesn't run the constructor again;
it only attaches another listener.

In the future we will likely introduce an API like `React.eager` that
is similar to `lazy` but eagerly calls the constructor. That gives us
the ability to call the constructor multiple times. E.g. to increase
the priority, or to retry if the first operation failed.
@gaearon gaearon mentioned this pull request Oct 23, 2018
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@wheelo wheelo commented Oct 25, 2018

Awesome

jetoneza added a commit to jetoneza/react that referenced this pull request Jan 23, 2019
Removes support for using arbitrary promises as the type of a React
element. Instead, promises must be wrapped in React.lazy. This gives us
flexibility later if we need to change the protocol.

The reason is that promises do not provide a way to call their
constructor multiple times. For example:

const promiseForA = new Promise(resolve => {
  fetchA(a => resolve(a));
});

Given a reference to `promiseForA`, there's no way to call `fetchA`
again. Calling `then` on the promise doesn't run the constructor again;
it only attaches another listener.

In the future we will likely introduce an API like `React.eager` that
is similar to `lazy` but eagerly calls the constructor. That gives us
the ability to call the constructor multiple times. E.g. to increase
the priority, or to retry if the first operation failed.
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