The equivalent to Python's json.dumps() in JavaScript is JSON.stringify() as in:

var jsonstr = JSON.stringify(someVariable);

Valid JSON doesn't contain structures like u'something', only something. If you really have a string like that, it's likely from Python via repr() or similar.

If you're trying to convert Python objects to JavaScript objects from within their respective environments, in Python you would convert them to a JSON encoded strings using json.dumps(), transfer the strings to the JavaScript environment, and then use JSON.parse() to convert them back into objects.

(Keep in mind that JSON doesn't understand anything beyond some basic types such as string, float, boolean, array, and key:value structures. For example, trying to transfer a Python datetime object is likely to get you string or a collection key:value pairs rather than an actual JavaScript Date object.)