Скачать или смотреть How to Wait for Promises to Resolve in JavaScript Callbacks

Discover how to manage asynchronous calls effectively in JavaScript, enabling you to wait for promises to resolve in callbacks.
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This video is based on the question https://stackoverflow.com/q/76768978/ asked by the user 'Nitor' ( https://stackoverflow.com/u/5530056/ ) and on the answer https://stackoverflow.com/a/76769593/ provided by the user 'Bergi' ( https://stackoverflow.com/u/1048572/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Managing Asynchronous JavaScript Calls with Promises

Asynchronous programming can often feel like navigating a maze, especially when handling multiple tasks and interactions simultaneously. If you've ever had to deal with callbacks while ensuring that certain promises resolve before executing further logic, you've likely encountered some frustrating moments. In this post, we'll walk through a specific problem encountered while developing a Steam bot and how to effectively manage asynchronous calls when dealing with promises and callbacks.

The Problem

Imagine you've created a bot using JavaScript to handle friend requests on Steam. You have a function steamAddFriend(user_steam_id) that sends a friend request and waits for a response. Upon changing the relationship with a user (for example, when they accept your friend request), you want to trigger a follow-up function sendUpdate2(user_steam_id) only after another function sendUpdate1(user_steam_id) has finished its processing. This situation often occurs in event-driven programming, where the order of execution matters, especially when using promises.

Here’s the essential snippet of the situation:

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The challenge lies in coordinating the flow such that sendUpdate2() waits for sendUpdate1() to finish, particularly when the bot handles multiple users simultaneously.

The Solution

To ensure that your friendRelationship callback waits appropriately for the completion of sendUpdate1(), you can utilize a lookup map to store current requests and their associated promises. Below, we’ll outline a clear process to follow.

Step 1: Create a Lookup Map

First, initialize a map to keep track of ongoing friend requests. This allows you to reference the promise associated with a given user once the relationship changes.

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Step 2: Modify the Friend Request Function

Next, modify your steamAddFriend(user_steam_id) function to store the promise returned by the function in the lookup map.

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This associates the promise generated by steamAddFriend for that specific Steam ID with the corresponding key in the openFriendRequests map.

Step 3: Handle the Callback Event

Now, adjust your friendRelationship callback to utilize the stored promise. When a friend request is accepted (i.e., the relationship changes), you can reference the corresponding promise from the map, ensuring that sendUpdate2(user_steam_id) gets executed only once sendUpdate1() has resolved.

Here’s what the updated code looks like:

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Final Thoughts

By using a lookup map, you efficiently manage the asynchronous flow of your bot, ensuring that updates proceed in the correct sequence. This approach can help avoid potential bugs or unexpected behavior when handling multiple users or friend requests simultaneously.

Using promises in this way allows for clean, readable code and more predictable behavior in your applications. This practice can be very helpful to streamline your JavaScript programming and make managing concurrent operations significantly easier.

For any developer working with asynchronous code, especially in response-driven contexts like chatbots or gaming APIs, mastering this approach is invaluable.