Скачать или смотреть Understanding How to Get the Eventually Returned Value for Promises in JavaScript

Discover how to properly handle promises in JavaScript, fixing common errors like "promise1.then is not a function" and effectively retrieving the returned values from promised-based functions.
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Understanding How to Get the Eventually Returned Value for Promises in JavaScript

Working with promises in JavaScript can sometimes be a challenge, especially when you're starting out. One common issue many developers encounter is the error message: "promise1.then is not a function." This often stems from not correctly invoking the function that returns the promise. In this post, we'll explore how to correctly handle promises to access their values, using a practical example.

The Problem Explained

Let's say we're trying to create two promises that each return a number: 19 from promise1 and 23 from promise2. You might write the initial code like this:

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

However, when we run this code, we get an error: "promise1.then is not a function". This error occurs because promise1 is a function that returns a promise, but we haven't called it correctly.

Solution: Correctly Invoking the Function

To solve this problem, you simply need to call promise1 like a function by adding parentheses (). This way, it will return the promise that we can then chain with then() to access the resolved value. Here’s the corrected code:

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

Full Corrected Code Example

Here's the complete and corrected code block for better clarity:

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

Summary

In conclusion, when working with promises in JavaScript, it’s essential to remember that if you define your promises as functions (like promise1 and promise2), you need to call them using parentheses to properly get the promised value. This small adjustment allows you to avoid the common pitfalls that new and experienced developers alike encounter.

By understanding this simple syntax, you can effectively leverage promises in your JavaScript applications, leading to cleaner and more effective asynchronous programming.

Whether you’re learning JavaScript or looking to brush up on your skills, mastering promises and how to handle them correctly is a key part of becoming a proficient developer. Happy coding!