Represent astral Unicode characters in Javascript, HTML or Ruby

Here is a symbol of an eight note: ♪

Its two-byte hex representation is 0x266A Show archive.org snapshot .

This card describes how to create a string with this symbol in various languages.

All languages

Since our tool chain (editors, languages, databases, browsers) is UTF-8 aware (or at least doesn't mangle bytes), you can usually get away with just pasting the symbol verbatim:

note = '♪'

This is great for shapes that are easily recognized by your fellow programmers.
It's not so great for non-distinct shapes like non-breaking spaces or hyphens of various lengths. For this, use the ways below.

Javascript, Coffeescript

Use the \u escape sequence:

note = '\u266A'

You can use Unicode escape sequences in both single and double quotes.

HTML

Use an entity:

♪

Ruby 1.9+

In modern Rubies you can use the \u escape sequence:

note = "\u266A"

Note that you must use double quotes. Unicode escape sequences are not parsed in a string with single quotes.

Ruby 1.8.7

There are no \u escape sequences in Ruby 1.8.7.

You either need to paste the '♪' symbol verbatim, or you can create a helper method that creates a string from an UTF-16 hex sequence:

class String
  def self.from_utf16_hex(sequence)
    parts = sequence.scan(/..../)
    parts = parts.map { |part| part.to_i(16) }
    parts.pack('U*')  
  end
end  

This lets you say:

String.from_utf16_hex('266a') # => '♪'
String.from_utf16_hex('266a266a') # => '♪♪'

This also works in modern Ruby versions.