React レンダー関数で Async/Await を正しく使用する方法は?

Understanding Async/Await in React Render Functions

Asynchronous programming, enabled by async/await syntax, is common in back-end development, such as Node.js, but can also be applied in front-end scenarios within React render functions.

Use Case: Geocoding with react-geocode

Consider a scenario where you need to obtain the place name for multiple locations using the react-geocode library and display them in a React table:

<code class="js">import React, { useEffect, useState } from 'react';
import Geocode from 'react-geocode';
import _ from 'lodash';

const GeocodeTable = ({ locations }) =&gt; {
  const [addresses, setAddresses] = useState([]);

  useEffect(() =&gt; {
    Promise.all(locations.map(async (loc) =&gt; {
      const address = await Geocode.fromLatLng(loc[0], loc[1]);
      return address.results[0].formatted_address;
    }))
    .then(results =&gt; setAddresses(results));
  }, [locations]);

  return (
    &lt;tbody&gt;
      {addresses.map((addr, idx) =&gt; (
        &lt;tr key={idx}&gt;
          &lt;td&gt;{addr}&lt;/td&gt;
          &lt;td&gt;Goa&lt;/td&gt;
          &lt;td&gt;asdsad&lt;/td&gt;
          &lt;td&gt;{_.get(loc, 'driverId.email', '')}&lt;/td&gt;
          &lt;td&gt;{_.get(loc, 'driverId.mobile', '')}&lt;/td&gt;
        &lt;/tr&gt;
      ))}
    &lt;/tbody&gt;
  );
};</code>

Mistakes to Avoid

In your original code, you attempted to use async/await directly within the map function of the render function. This is not supported and will result in an empty return.

Best Practices

• Separate Data Fetching from Displaying: The recommended approach is to separate data fetching from rendering. Use a parent component to perform asynchronous operations (like geocoding) and conditionally render a child component when the data is available.
• Use Memoization: To optimize performance, consider using memoization techniques, such as useMemo in the parent component, to avoid redundant data fetching.
• TypeScript Support: If using TypeScript, consider defining types for the geocoding results to improve type safety and avoid potential errors.

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