Q:

Convert to full unicode string

How can I convert a string from \uD83D\uDE00 to full \U0001f603?
json_encode() only converts to the first option...
$str = '';
$encode = json_encode($str);
var_dump($encode);

// string(14) ""\ud83d\ude03""

A:

Assuming you have the Intl extension installed, this is easy enough to do with one of its built-in transliterators:
<?php
$str = "";
echo transliterator_create("Any-Hex/C")->transliterate($str);

Output:
\U0001F603

