Printing emojis with JavaScript and HTML

Question

Why does this work:

<p id="emoji">&#x1f604;</p> 

And this doesn't:

document.getElementById("emoji").innerHTML = String.fromCharCode(parseInt('1f604', 16)); 

Answer 1

A 'char' in JS terms is actually a UTF-16 code unit, not a full Unicode character. (This sad state of affairs stems from ancient times when there wasn't a difference*.) To use a character outside of the Basic Multilingual Plane you have to write it in the UTF-16-encoded form of a surrogate pair of two 16-bit code units:

String.fromCharCode(0xD83D, 0xDE04) 

In ECMAScript 6 we will get some interfaces that let us deal with strings as if they were full Unicode code points, though they are incomplete and are only a façade over the String type which is still stored as a code unit sequence. Then we'll be able to do:

String.fromCodePoint(0x1F604) 

See this question for some polyfill code to let you use this feature in today's browsers.

(*: When I get access to a time machine I'm leaving Hitler alone and going back to invent UTF-8 earlier. UTF-16 must never have been!)