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Learn how to execute multiple `fetch` API calls in sequence while maintaining the order of responses using JavaScript. This guide simplifies the process for you.
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Running Multiple fetch Calls in Order: A JavaScript Guide

When working with web APIs, it's common to need to fetch data based on a list of parameters. However, a frequent challenge arises when trying to run multiple fetch calls in a specific order while maintaining the sequence of the returned data. If you have encountered a scenario where your fetch calls execute out of sequence, this guide is for you! Let’s break down the problem and see how to address it effectively in JavaScript.

The Problem

Imagine you have an array of sizes, and for each size, you would like to make a fetch API call that returns specific data based on the size. The issue arises when you attempt to push these responses into a larger array, as they may not maintain the order of the original array due to the asynchronous nature of JavaScript's fetch calls. Below is an example of what that code might look like:

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In this code, while you're looping through sizeOptionsArr, the asynchronous nature of the fetch call results in the index being logged in a random order. This behavior is due to the fact that the fetch requests are not synchronized, leading to responses being returned as they complete.

The Solution

To ensure that all fetch calls run and complete in the order of the original array while allowing you to gather the responses efficiently, you can utilize Promise.all. This method runs all the promises in parallel but collects the results in an ordered array, which matches the order of your input.

Step-by-Step Solution

Map Your Array to Fetch Promises: Convert each size option into a fetch promise. This is done using the map() function, which creates a new array of promises instead of running them immediately.

Use Promise.all: This will run all the fetch calls in parallel, and after all of them resolve, it will provide a consolidated response collected in the correct order.

Here’s how you can implement this solution:

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Benefits of This Approach

Maintains Order: The fetched results maintain the order of the original array, ensuring you get a consistent structure.

Efficiency: By running requests in parallel, the total execution time is minimized compared to running them sequentially.

Error Handling: You can easily manage errors in one place with .catch(), improving the robustness of your code.

Conclusion

By following the approach outlined in this guide, you can effectively run multiple fetch API calls in order while collecting the responses in a structured manner. Utilizing Promise.all to handle your fetch requests allows you to work seamlessly with asynchronous data fetching in JavaScript, creating a more efficient and maintainable codebase.

If you have any more questions or need further assistance, feel free to ask. Happy coding!