JS Practice — Built-in Objects

String.prototype.toLocaleUpperCase() — numbers unchanged

📖 Usage Example

'hello'.toLocaleUpperCase()   // → 'HELLO'
'world'.toLocaleUpperCase()   // → 'WORLD'
'abc123'.toLocaleUpperCase()  // → 'ABC123'

Use toLocaleUpperCase() to convert a string to uppercase using the locale-specific rules of the host environment.

String.prototype.toLocaleUpperCase() — Non-Letter Characters

Digits and symbols are not affected by toLocaleUpperCase().

Challenge: Implement upperLettersOnly(str) that uppercases a string with mixed letters and numbers.

upperLettersOnly('abc123') // → 'ABC123'

💡 Hints (1)