How to Iterate over a Nested JS Object in React with useState and Axios

Learn how to effectively iterate over a nested JavaScript object in a React component, using useState and Axios to manage API responses.
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How to Iterate over a Nested JS Object in React with useState and Axios

When working with nested JSON responses in React, especially when you're fetching data using libraries such as Axios, it can be a bit challenging to extract the information you need. In this guide, we'll address a common problem: how to iterate over a nested JavaScript object to access specific properties within it.

The Problem

Imagine that you are using useState to hold the data fetched via an API call. When you pass this data to a component to render it, you're faced with a scenario where the data structure is nested, and you need to extract information from it.

Example Code

Here’s a sample setup using useState and Axios for fetching data:

[[See Video to Reveal this Text or Code Snippet]]

You then pass this state to a component like this:

[[See Video to Reveal this Text or Code Snippet]]

However, with the structure of the response, you might encounter issues trying to access specific parts of the object, leading to a console output that looks like this:

[[See Video to Reveal this Text or Code Snippet]]

Expected Response Structure

The returned data might look something like this:

[[See Video to Reveal this Text or Code Snippet]]

Your task is to loop over the properties to get to myPasser->result->list and print each list element.
Solution

The key to solving this problem is to use nested mapping. You need to first access the higher-level properties, then drill down into the nested properties.

Here's a refactored component:

Step-by-Step Breakdown

Extract Entries
Start by using Object.entries to loop over the properties of the received object.

Access Nested Properties
Within this loop, access the nested result and list properties using a second map().

Updated KlineInfo Component

Here’s the restructured component that accomplishes the iteration over the nested object:

[[See Video to Reveal this Text or Code Snippet]]

Code Explanation

Object.entries(myPasser) loops through each key/value pair of the myPasser object.

For each value, we access value.result.list and map over it.

listItem will represent each sub-array. We convert each listItem into a string format using JSON.stringify.

Render Output

You’ll end up with an output that displays every element from the list array in a readable format. You can further customize how you display this data based on your UI needs.
Conclusion

Iterating over nested JavaScript objects can be complicated, but understanding how to leverage nested map() functions makes it manageable. When you are fetching data from an API and working with complex data structures, spend time visualizing the data and anticipate how you will access it. This ensures a smoother development process and a better user experience.

Now, the next time you encounter a nested object response, you can confidently iterate through it and extract the information you need!

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