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svelte/documentation/tutorial/08-stores/03-readable-stores/text.md

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---
title: Readable stores
---
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 an initial value, which can be `null` or `undefined` if you don't have one yet. The second argument 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.
```js
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export const time = readable(new Date(), function start(set) {
const interval = setInterval(() => {
set(new Date());
}, 1000);
return function stop() {
clearInterval(interval);
};
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});
```