Unexpected Error in JavaScript: JSON.stringify is not a function Learn how to fix it with these code examples.

Table of content

  1. What is JSON?
  2. What is JSON.stringify?
  3. Common causes of "JSON.stringify is not a function" error
  4. How to fix the error?
  5. Example 1: Fixing "JSON.stringify is not a function" error
  6. Example 2: Fixing the error with a custom replacer function
  7. Conclusion

What is JSON?

JSON, short for JavaScript Object Notation, is a lightweight data interchange format that is designed to be easy for humans to read and write, and easy for machines to parse and generate. It was invented by Douglas Crockford in the early 2000s as a simpler alternative to the more verbose XML format that was popular at the time.

JSON is widely used in web development to send and receive data between clients and servers. It is particularly well-suited for use with JavaScript, as it can be easily converted to and from JavaScript objects using the built-in JSON.parse() and JSON.stringify() functions.

JSON data is typically stored in a hierarchical, tree-like structure consisting of key-value pairs or arrays, with curly braces {} denoting objects and square brackets [] denoting arrays. For example, a simple JSON object describing a person might look like this:

    "name": "Alice",
    "age": 28,
    "address": {
        "city": "New York",
        "state": "NY",
        "zip": "10001"
    "hobbies": [

In this example, the object has four key-value pairs: "name" with the value "Alice", "age" with the value 28, "address" with the value of another nested object containing the person's address, and "hobbies" with the value of an array of the person's hobbies.

Understanding JSON and how to use JSON.stringify() and JSON.parse() functions is essential for web developers who want to work with data in their applications.

What is JSON.stringify?

JSON.stringify is a built-in function in JavaScript that converts a JavaScript object into a JSON string. JSON, which stands for JavaScript Object Notation, is a lightweight data format used to store and exchange data between a server and a web application. It is widely used in modern web development for sending and receiving data from a server in a format that is easy to parse and manipulate.

The JSON.stringify function takes two arguments: the object you want to convert to a JSON string, and an optional replacer function or array that allows you to filter or modify the output. The resulting JSON string can be saved or sent as a text file, or used in a web application to display or manipulate data.

JSON.stringify is an important function in web development, as it provides a way to transfer data between different programming languages and platforms. It is also widely used in APIs and web services, where data must be exchanged between different applications in a standardized format.

In summary, JSON.stringify is a key function in JavaScript that enables developers to convert JavaScript objects to JSON strings for data transfer and manipulation. Its simplicity and ease of use make it a powerful tool in modern web development, and understanding how it works is essential for anyone working with JavaScript and web applications.

Common causes of “JSON.stringify is not a function” error

If you are a programmer working with JavaScript, you may have come across the error message: "Unexpected Error. JSON.stringify is not a function!" This error can be frustrating and confusing, but fortunately, it can be solved with some simple solutions. Let's explore the common causes of this error.

One of the most common causes of this error is when you are trying to stringify an undefined or null value. JSON.stringify only works with data that can be converted to a string, so if you try to stringify an undefined or null value, it will result in this error.

Another cause of this error is when there is a conflict between different versions of JavaScript. Sometimes, newer versions of JavaScript have introduced new functionalities that older versions do not support. This can cause conflicts when running your code, resulting in the "JSON.stringify is not a function" error.

Finally, it is possible that the JSON object has not been initialized properly. This object is used to work with JSON data in JavaScript, so if it has not been properly initialized, it can cause this error.

In conclusion, the "JSON.stringify is not a function" error can be caused by a variety of factors. By understanding the common causes of this error, you can troubleshoot and fix it more easily.

How to fix the error?

If you encounter the error "JSON.stringify is not a function" in your JavaScript code, don't worry. This error message indicates that the object you are trying to parse is not a valid JSON object. Fortunately, there are a few ways to fix this error.

First, make sure that the object you are trying to parse is a valid JavaScript object or array. Check the syntax and make sure that all the properties and values are correctly formatted.

If this does not solve the problem, try using the built-in JSON.parse() function instead of JSON.stringify(). JSON.parse() converts a JSON text into a JavaScript object, and can handle more complex data types.

For example, if you have a JSON string that looks like this:

var json_string = '{"name": "John", "age": 30}';

You can convert it to a JavaScript object like this:

var person = JSON.parse(json_string);
console.log(person.name); // Output: John
console.log(person.age); // Output: 30

If you still encounter the error, check your JavaScript version. JSON.stringify() is only supported in newer versions of JavaScript, so make sure that your version supports this function.

In conclusion, the "JSON.stringify is not a function" error message can be intimidating, but it is easy to fix with a few simple steps. By ensuring that the object you are trying to parse is valid, using JSON.parse() instead of JSON.stringify(), and checking your JavaScript version, you can avoid this error and create successful JavaScript programs.

Example 1: Fixing “JSON.stringify is not a function” error

If you are working with JavaScript and you encounter the error "JSON.stringify is not a function", don't panic! This error occurs when the JSON object is not recognized by the browser or is not properly installed. Luckily, there are different ways to fix this error. Here's an example of how to resolve this error using code:

if (typeof JSON.stringify !== "function") {
    JSON.stringify = function(obj) {
        var replacer = function(key, value) { return value === undefined ? null : value; };
        return JSON.stringify(obj, replacer, 2);

In this example, we check if the JSON.stringify function exists. If it does not, we redefine it with a replacer function that replaces any undefined values with null. We also format the JSON with an indentation of two spaces to make it easier to read.

It's important to note that although this code fixes the issue, it's not a permanent solution. It's better to check for browser compatibility and make sure that the necessary libraries are installed in the first place. By keeping updated with the latest versions of JavaScript and libraries, you can ensure that your code is always up to date and less prone to errors.

So, if you encounter the error "JSON.stringify is not a function", don't worry! Use this example code and keep developing your coding skills. Remember, programming is all about solving problems, and errors like this are just another puzzle to solve.

Example 2: Fixing the error with a custom replacer function

Another way to fix the "JSON.stringify is not a function" error is by using a custom replacer function. A replacer function is a function that can modify the behavior of JSON.stringify by replacing the default serialization of an object with a custom serialization.

Here's an example of how to use a custom replacer function to fix the error:

const obj = {
    name: "John",
    age: 30,
    city: "New York",
    toJSON: function() {
        return {
            name: this.name,
            age: this.age

const jsonStr = JSON.stringify(obj, function(key, value) {
    if (key === "age") {
        return undefined;
    return value;


In this example, we define an object obj with three properties: name, age, and city. We also define a custom toJSON method on the object that returns an object with only the name and age properties.

To fix the "JSON.stringify is not a function" error, we use the JSON.stringify method with a custom replacer function as the second argument. In our custom replacer function, we check if the key is "age". If it is, we return undefined, which will omit the "age" property from the JSON string. If it isn't, we return the original value.

When we run the code, the JSON string is generated without the "age" property:


Using a custom replacer function offers more control over the serialization of an object and can be useful in scenarios where certain properties need to be omitted or customized.


In , the error message "JSON.stringify is not a function" is a common issue that can be frustrating for JavaScript programmers. However, it is a problem that can easily be resolved with the right techniques. By checking the syntax of your code and ensuring that your objects are correctly formatted as JSON, you can avoid this error and improve the overall functionality of your program.

It's worth noting that JSON has become an incredibly popular format for data exchange due to its simplicity and widespread support across programming languages. As such, understanding how to work with JSON objects and the associated APIs is a valuable skill for any developer.

With the troubleshooting tips and code examples outlined in this article, you should have a solid understanding of how to handle this error and navigate similar issues that may arise in your programming journey. Remember to stay patient and persistent when debugging your code and continue to build your skills and knowledge as you tackle more complex projects.

As an experienced software engineer, I have a strong background in the financial services industry. Throughout my career, I have honed my skills in a variety of areas, including public speaking, HTML, JavaScript, leadership, and React.js. My passion for software engineering stems from a desire to create innovative solutions that make a positive impact on the world. I hold a Bachelor of Technology in IT from Sri Ramakrishna Engineering College, which has provided me with a solid foundation in software engineering principles and practices. I am constantly seeking to expand my knowledge and stay up-to-date with the latest technologies in the field. In addition to my technical skills, I am a skilled public speaker and have a talent for presenting complex ideas in a clear and engaging manner. I believe that effective communication is essential to successful software engineering, and I strive to maintain open lines of communication with my team and clients.
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