Swapcase string

Isabelle Viktoria Maciohsek · JavaScript, String · Nov 15, 2020

Creates a string with uppercase characters converted to lowercase and vice versa.

  • Use the spread operator (...) to convert str into an array of characters.
  • Use String.prototype.toLowerCase() and String.prototype.toUpperCase() to convert lowercase characters to uppercase and vice versa.
  • Use Array.prototype.map() to apply the transformation to each character, Array.prototype.join() to combine back into a string.
  • Note that it is not necessarily true that swapCase(swapCase(str)) === str.
const swapCase = str =>
  [...str]
    .map(c => (c === c.toLowerCase() ? c.toUpperCase() : c.toLowerCase()))
    .join('');
swapCase('Hello world!'); // 'hELLO WORLD!'

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