Answers by Sentry

How do you loop inside React JSX?

Naveera A.

The Problem

You have a set of elements, and you’d like to loop over them to generate a JSX partial.

In templating languages, you can write a for loop directly inside the template. For example, you can use the following code to loop over a list in Jinja:

{% for i in range(11) %}
    <li>{{ i }}</li>
{% endfor %}

How can you do the same thing using JSX?

The Solution

Two ways you can loop inside JSX are using traditional loops or using the map() method.

Using Traditional Loops

If you have a set of elements, you can use normal JavaScript for, for of, and for in loops outside the return block.

Inside the return block, you can use the resulting array.

You can loop over an array and create JSX partials like so:

import React from "react";

function App() {
  const seasons = ["Spring", "Summer", "Autumn", "Winter"];

  let seasonsList = [];

  seasons.forEach((season, index) => {
    seasonsList.push(<li key={index}>{season}</li>);
  });

  return (
    <div>
      <h2>Seasons of the year</h2>
      <ul>{seasonsList}</ul>
    </div>
  );
}

export default App;

Using the map() Method

You can use the map() method on an array to loop through the elements and create components, or generate JSX, inside the return block.

import React from "react";

function App() {
  const seasons = ["Spring", "Summer", "Autumn", "Winter"];

  return (
    <div>
      <h2>Seasons of the year</h2>
      <ul>
        {seasons.map((season) => (
          <li key={season.id}>{season}</li>
        ))}
      </ul>
    </div>
  );
}

export default App;

Many developers prefer using map() to loop over arrays.

Get Started With Sentry

Get actionable, code-level insights to resolve React performance bottlenecks and errors.

  1. Create a free Sentry account

  2. Create a React project and note your DSN

  3. Grab the Sentry React SDK

  npm install @sentry/react
  1. Configure your DSN
  import React from "react";
  import ReactDOM from "react-dom";
  import * as Sentry from "@sentry/react";
  import App from "./App";

  Sentry.init({
    dsn: "https://<key>@sentry.io/<project>"
  });

  ReactDOM.render(<App />, document.getElementById("root"));

Check our documentation for the latest instructions.

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