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19 lines
849 B
19 lines
849 B
6 years ago
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---
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title: Readable stores
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---
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Not all stores should be writable by whoever has a reference to them. For example, you might have a store representing the mouse position or the user's geolocation, and it doesn't make sense to be able to set those values from 'outside'. For those cases, we have *readable* stores.
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Click over to the `stores.js` tab. The first argument to `readable` is a `start` function that takes a `set` callback and returns a `stop` function. The `start` function is called when the store gets its first subscriber; `stop` is called when the last subscriber unsubscribes. The second (optional) argument is the initial value.
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```js
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export const time = readable(function start(set) {
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const interval = setInterval(() => {
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set(new Date());
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}, 1000);
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return function stop() {
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clearInterval(interval);
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};
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}, new Date());
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```
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