30-seconds-of-code/snippets/extend-hex.md

3-digit hexcode to 6-digit hexcode

Use Array.map(), split() and Array.join() to join the mapped array for converting a three-digit RGB notated hexadecimal color-code to the six-digit form. Array.slice() is used to remove # from string start since it's added once.

const extendHex = shortHex =>
  '#' + shortHex.slice(shortHex.startsWith('#') ? 1 : 0).split().map(x => x+x).join()
// convertHex('#03f') -> '#0033ff'
// convertHex('05a') -> '#0055aa'