Скачать или смотреть How to Call HTTP POST Recursively in Angular 9 Using Async/Await

Discover how to handle batch requests in Angular 9 with recursive HTTP POST calls using async/await. Ensure your API calls do not run simultaneously and maintain control over the execution flow.
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This video is based on the question https://stackoverflow.com/q/66102298/ asked by the user 'snowflakes74' ( https://stackoverflow.com/u/819073/ ) and on the answer https://stackoverflow.com/a/66102389/ provided by the user 'Thomas Sablik' ( https://stackoverflow.com/u/4645334/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Handling Recursive HTTP POST Requests in Angular 9

When working with APIs in Angular, especially when making multiple requests, you might run into a situation where your backend system executes simultaneous calls instead of waiting for previous ones to complete. This can lead to unexpected behavior and issues like race conditions. In this guide, we’ll explore how to correctly handle recursive HTTP POST requests in Angular 9, ensuring that each call waits for the previous one to complete before starting the next one.

The Problem

Imagine you have a requirement to send batches of data to an external API. However, each batch can only contain a limited number of items (in this case, 5). When you try to submit these batches one after the other using a loop, all the HTTP POST requests are sent at once. This is exactly what our code example illustrates:

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In the above snippet, if you have 10 batches to send, your API can end up processing all of them simultaneously, leading to potential issues on the server side. We need a way to ensure that each batch is sent in sequence.

The Solution: Using Async/Await

By utilizing async/await, we can create a more controlled flow for our API calls. This allows us to wait for each request to complete before proceeding to the next one. Here’s how you can modify your submitReport method to achieve this:

Step 1: Modify the Submit Method to Use Async

First, we need to declare our submitReport method as async. This tells JavaScript that we will be using await within this method.

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Step 2: Use Promises with the HTTP Service

In the updated submitReport method:

We use await to pause the execution until the promise returned by submitReport resolves.

We wrap the API call in a try...catch block to gracefully handle any errors.

Example Function

To illustrate this concept further, here's a simple async function that uses a promise:

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

Conclusion

By modifying your HTTP POST request to use async/await, you can ensure that each API call completes before the next one starts. This is especially useful in scenarios where your API can only handle a limited number of requests at a time.

With these changes, you’ll have a more robust batch submission method that reduces the risk of overwhelming your backend service. By neatly controlling the flow of your API calls, you can maintain a smooth user experience and avoid unexpected errors in your application.

Implementing async methods might seem challenging at first, but once you understand the flow, you'll appreciate the power it brings to your code.