How to convert an x-www-form-urlencoded string to JSON?

This is a core module of Node.js now: https://nodejs.org/api/querystring.html#querystring_querystring_parse_str_sep_eq_options

var qs = require('querystring')

var json = qs.parse('why=not&sad=salad')
    // { why: 'not', sad: 'salad' }

Works with encoded characters too:

var json2 = qs.parse('http%3A%2F%2Fexample.com&sad=salad')
    // { url: 'http://example.com', sad: 'salad' }