2775. Undefined to Null 🔒 

Description

Given a deeply nested object or array obj, return the object obj with any undefined values replaced by null.

undefined values are handled differently than null values when objects are converted to a JSON string using JSON.stringify(). This function helps ensure serialized data is free of unexpected errors.

Example 1:

Input: obj = {"a": undefined, "b": 3}
Output: {"a": null, "b": 3}
Explanation: The value for obj.a has been changed from undefined to null

Example 2:

Input: obj = {"a": undefined, "b": ["a", undefined]}
Output: {"a": null,"b": ["a", null]}
Explanation: The values for obj.a and obj.b[1] have been changed from undefined to null

Constraints:

obj is a valid JSON object or array
2 <= JSON.stringify(obj).length <= 10⁵

Solutions

Solution 1

TypeScript

function undefinedToNull(obj: Record<any, any>): Record<any, any> {
    for (const key in obj) {
        if (typeof obj[key] === 'object') {
            obj[key] = undefinedToNull(obj[key]);
        }
        if (obj[key] === undefined) {
            obj[key] = null;
        }
    }
    return obj;
}

/**
 * undefinedToNull({"a": undefined, "b": 3}) // {"a": null, "b": 3}
 * undefinedToNull([undefined, undefined]) // [null, null]
 */