Скачать или смотреть Solving the TypeError When Using new Map() with JSON Strings in JavaScript

Learn how to fix the common `TypeError` in JavaScript when trying to create a `Map` from a JSON string. This post provides a clear solution and explanation.
---
This video is based on the question https://stackoverflow.com/q/66286837/ asked by the user 'coderman1234' ( https://stackoverflow.com/u/15134005/ ) and on the answer https://stackoverflow.com/a/66286854/ provided by the user 'Lionel Rowe' ( https://stackoverflow.com/u/8318731/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: new Map() returns error when going through JSON string

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding the TypeError with new Map() and JSON Strings

When working with JavaScript, you may encounter various challenges, especially when dealing with data formats like JSON. A common issue that many developers face is encountering a TypeError when trying to create a Map from a JSON string. This error might leave you puzzled, especially when everything seems fine at first glance. Let's dive into the problem and understand how to solve it effectively.

The Problem

Imagine you have a JSON string like this:

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

You might expect that creating a Map from this string would be straightforward. However, when you attempt to run the following code:

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

You receive an error message that looks like this:

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

What Went Wrong?

The issue arises because the constructor for a Map requires an array of entries in the form of [key, value] tuples. However, when you use JSON.parse(str), you get a plain JavaScript object rather than a format that the Map constructor understands.

The Solution

To successfully create a Map from a JSON string, you need to transform the object into an array of entries. This can be done easily using the Object.entries() method. Here’s how you can do it:

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

Explanation of the Solution

JSON.parse(str): This will convert the JSON string into a JavaScript object.

Object.entries(): This method takes the object and returns an array of its own enumerable string-keyed property [key, value] pairs.

new Map(): Finally, you can pass this array of entries to the Map constructor to create a Map instance successfully.

Benefits of Using This Approach

Prevents Errors: Avoids the TypeError that occurs when directly passing an object to the Map constructor.

Flexibility: Allows for straightforward changes if the structure of the JSON changes in the future.

Readability: Using Object.entries() makes your intention clear — you are converting an object into a two-dimensional array suitable for creating a Map.

Conclusion

In conclusion, when working with JSON strings in JavaScript and needing to convert them into a Map, remember that simply parsing the JSON is not enough. Use Object.entries() to transform the object into an appropriate format. With this workaround, you can avoid the common TypeError and work smoothly with Map objects.

Additional Tips

Always ensure your JSON string is well-formed (valid JSON).

Debugging can be efficiently done by logging the intermediate outputs such as the result of JSON.parse() to understand the data structure you are working with.

By following this guide, you should be able to handle similar issues with ease and gain deeper insights into working effectively with JavaScript objects and maps.