Kebab file names

snippets/use-interval.md

@@ -0,0 +1,50 @@
+---
+title: React useInterval hook
+tags: hooks,effect
+author: chalarangelo
+cover: digital-nomad-13
+firstSeen: 2019-08-21T13:18:52+03:00
+lastUpdated: 2020-11-16T14:17:53+02:00
+---
+
+Implements `setInterval()` in a declarative manner.
+
+- Create a custom hook that takes a `callback` and a `delay`.
+- Use the `useRef()` hook to create a `ref` for the callback function.
+- Use a `useEffect()` hook to remember the latest `callback` whenever it changes.
+- Use a `useEffect()` hook dependent on `delay` to set up the interval and clean up.
+
+```jsx
+const useInterval = (callback, delay) => {
+  const savedCallback = React.useRef();
+
+  React.useEffect(() => {
+    savedCallback.current = callback;
+  }, [callback]);
+
+  React.useEffect(() => {
+    const tick = () => {
+      savedCallback.current();
+    }
+    if (delay !== null) {
+      let id = setInterval(tick, delay);
+      return () => clearInterval(id);
+    }
+  }, [delay]);
+};
+```
+
+```jsx
+const Timer = props => {
+  const [seconds, setSeconds] = React.useState(0);
+  useInterval(() => {
+    setSeconds(seconds + 1);
+  }, 1000);
+
+  return <p>{seconds}</p>;
+};
+
+ReactDOM.createRoot(document.getElementById('root')).render(
+  <Timer />
+);
+```