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How can I convert a nested JavaScript object into a JSON string while skipping undefined values?

Asked on Oct 17, 2025

Answer

To convert a nested JavaScript object into a JSON string while skipping undefined values, you can use the `JSON.stringify` method with a custom replacer function. The replacer function allows you to filter out undefined values during the conversion process.

<!-- BEGIN COPY / PASTE -->
        const obj = {
            name: "Alice",
            age: undefined,
            details: {
                hobbies: ["reading", "gaming"],
                address: undefined
            }
        };

        const jsonString = JSON.stringify(obj, (key, value) => {
            return value === undefined ? undefined : value;
        });

        console.log(jsonString); // Output: {"name":"Alice","details":{"hobbies":["reading","gaming"]}}
        <!-- END COPY / PASTE -->

Additional Comment:

The `JSON.stringify` method accepts a replacer function as its second argument.
The replacer function checks if a value is undefined and skips it by returning undefined.
This approach ensures that undefined values are not included in the resulting JSON string.

✅ Answered with JavaScript best practices.

Ask any question about JavaScript here... and get an instant response.

How can I convert a nested JavaScript object into a JSON string while skipping undefined values?

Asked on Oct 17, 2025

Answer

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