JS Practice — Built-in Objects

String.prototype.replace() — replace with function

📖 Usage Example

'foo bar foo'.replace('foo', 'baz')    // → 'baz bar foo'
'hello'.replace(/[aeiou]/g, '*')       // → 'h*ll*'

Use replace() to replace the first occurrence of a pattern; use a /g regex to replace all occurrences.

String.prototype.replace() — Replacer Function

The second argument can be a function. It receives the matched substring and returns the replacement.

Challenge: Implement doubleNumbers(str) that doubles every digit found in the string.

doubleNumbers('a1b2') // → 'a2b4'

💡 Hints (2)