Characters

Q: A string is "a series of characters"... but what is a character?

A: a character is a number (or character code) that stands for a symbol.

(Some characters stand for unprintable symbols like newline or tab or bell.)

ASCII and ye shall receive-ski

• ASCII: American Standard Code for Information Interchange
• Invented in 1963

(image from Wikimedia Commons)

Unicode

• ASCII only goes from 0 to 127
• Unicode is the same as ASCII for values from 0 and 127
  • but Unicode goes a lot higher
• Currently more than 130,000 characters, including symbols for
  • 139 modern and historic scripts
  • accents and other diacritics
  • various mathematical ∞, currency £, and cultural ☮ symbols
  • emoji 😂

Unicode Strings

JavaScript strings are Unicode

• technically, JS uses the UTF-16 encoding in memory
• and the UTF-8 encoding for text files

That means you can use emoji in your JavaScript programs!

Like this:

"😂".repeat(20)

(sadly this doesn't work in Windows PowerShell, but it does work in Atom+node, like this:)

  response.setHeader('content-type', 'text/html');
  response.write('<meta charset="UTF-8">')
  response.write("😂".repeat(20));
  response.end();

Unicode Encodings

• UTF-32 is a fixed-width encoding for Unicode
  • every character is 32 bits long
• UTF-8 is a variable-width encoding for Unicode
  • all ASCII characters are one byte long (8 bits)
  • other characters are up to four bytes long (32 bits)
  • used for text files
• UTF-16 is a variable-width encoding for Unicode
  • every character is either 16 or 32 bits long
  • used by JavaScript at runtime

[TODO: diagrams]

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