How to generate a JSON object dynamically with duplicate keys?

Question

I know this will sound impossible but my boss told me I MUST send a JSON over an AJAX post call with jQuery that MUST HAVE DUPLICATE KEYS. the problem is that if I write som

Answer 1

A Javascript object with duplicate keys is not a Javascript object. In fact, it is no more than a figment of your imagination. It is totally impossible.

The only way to do this is with an array:

{
     "key1" : "value1",
     "key2" : ["value2", "value3", "value4"],
     "key3" : "value5"
}

jQuery will convert this into key1=value1&key2%5B%5D=value2&key2%5B%5D=value3&key2%5B%5D=value4&key3=value5

This is genuinely the only way to do this.* Is there a reason why your code cannot generate valid JSON?

_{* Except for writing your own parser that handles invalid JSON. But that would be breathtakingly stupid.}