JSON to text in JavaScript

textFromJson.js

function textFromJson(json) {
    if (json === null || json === undefined) {
      return '';
    }
    if (!Array.isArray(json) && !Object.getPrototypeOf(json).isPrototypeOf(Object)) {
      return '' + json;
    }
    const obj = {};
    for (const key of Object.keys(json)) {
        obj[key] = textFromJson(json[key]);
    }
    return Object.values(obj).join(' ');
}

I use this to extract text from json specifically for full text searches on log dumps