Regular Expressions: Hex Codes

• Computers internally store text as numbers. As a shorthand, we usually write those numbers out as hexadecimal codes.

• >

  /\x41/.test('A'); // 'A' is x41

  Result:

  true

• For example, capital letter "A" has the hex code x41. Regular expressions and most programming languages allow this "x" syntax. To match "A" in a regex, we can write \x41.

• >

  /\x41/.test('an apple');

  Result:

  false

• >

  /\x41/.test('CATS ARE GOOD');

  Result:

  true

• x42 is "B".

• >

  /\x42/.test('An apple');

  Result:

  false

• >

  /\x42/.test('Both apples');

  Result:

  true

• Each digit can be a number, or a letter between "a" and "f". For example, "M" is x4d in hex. (The x isn't a hex digit; it's telling us that this is a hex code.)

• >

  /\x4d/.test('M');

  Result:

  true

• There's a hex code for each character, even ones that aren't letters. "?" is x3f and "!" is x21.

• >

  /\x3f/.test('?');

  Result:

  true

• >

  /\x21/.test('!');

  Result:

  true

• We can use hex codes to match symbols that you may not be able to type.

• The letter "ø" doesn't appear on an US-English keyboard. To match that letter, we can use its hex code \xf8.

• >

  /\xf8/.test('søt katt');

  Result:

  true

• If we have a keyboard that can type "ø", we can put it directly in a regex.

• >

  /ø/.test('smørbrød');

  Result:

  true

• Be careful: the syntax \x can only be followed by exactly two digits. Anything after the two digits will be a different part of the regex.

• >

  /\x41d/.test('A');

  Result:

  false

• >

  /\x5Ad/.test('Zd'); // "Z" is x5A

  Result:

  true

• If we write an \x with only one digit, it's no longer a character code. Instead, the \x matches literal "x" characters.

• >

  /\x4/.test('x4'); // This is probably a mistake with \x!

  Result:

  true

• Hexadecimal digits can be any character from 0-9, a-f, or A-F. If we use the wrong characters, the \x will match literal "x" again.

• >

  /\xfg/.test('xfg');

  Result:

  true