Shouldn't JSON.stringify escape Unicode characters?

Question

I have a simple test page in UTF-8 where text with letters in multiple different languages gets stringified to JSON:

http://jsfiddle.net/Mhgy5/

HTML:

<textarea id="txt">
検索 • Busca • Sök • 搜尋 • Tìm kiếm • Пошук • Cerca • Søk • Haku • Hledání • Keresés • 찾기 • Cari • Ara • جستجو • Căutare • بحث • Hľadať • Søg • Serĉu • Претрага • Paieška • Poišči • Cari • חיפוש • Търсене • Іздеу • Bilatu • Suk • Bilnga • Traži • खोजें
</textarea>
<button id="encode">Encode</button>
<pre id="out">
</pre>

JavaScript:

​$("#encode").click(function () {
    $("#out").text(JSON.stringify({ txt: $("#txt").val() }));
}).click();
​

While I expect the non-ASCII characters to be escaped as \uXXXX as per the JSON spec, they seem to be untouched. Here's the output I get from the above test:

{"txt":"検索 • Busca • Sök • 搜尋 • Tìm kiếm • Пошук • Cerca • Søk • Haku • Hledání • Keresés • 찾기 • Cari • Ara • جستجو • Căutare • بحث • Hľadať • Søg • Serĉu • Претрага • Paieška • Poišči • Cari • חיפוש • Търсене • Іздеу • Bilatu • Suk • Bilnga • Traži • खोजें\n"}

I'm using Chrome, so it should be the native JSON.stringify implementation. The page's encoding is UTF-8. Shouldn't the non-ASCII characters be escaped?

What brought me to this test in the first place is, I noticed that jQuery.ajax doesn't seem to escape non-ASCII characters when they appear in a data object property. The characters seem to be transmitted as UTF-8.

Answer 1

Indeed JSON.stringify does not escape utf8:

JSON.stringify({a:"Привет!"})
{"a":"Привет!"}

But I had an issue when stroring that JSON via Perl DBD::Mysql and then retrieving it back. I found it is safer to follow reccomendation to escape all non-ascii and non-visible characters by \uXXXX. Here is how

function jsonEscapeUTF(s) {return s.replace(/[^\x20-\x7F]/g, x => "\\u" + ("000"+x.codePointAt(0).toString(16)).slice(-4))}

jsonEscapeUTF(JSON.stringify({a:"Привет!"}))
"{"a":"\u041f\u0440\u0438\u0432\u0435\u0442!"}"

Hopefully it will be helpful.