JS Practice — Built-in Objects

String.prototype.substring() — extract first N chars

📖 Usage Example

const str = 'Hello, World!'
str.substring(7, 12)   // → 'World'
str.substring(5, 2)    // → 'llo' (args swapped)
str.substring(7)       // → 'World!'

Use substring() to extract characters between two indices, automatically swapping them if start is greater than end.

String.prototype.substring() — First N Chars

str.substring(0, n) extracts the first n characters.

Challenge: Implement firstN(str, n) that returns the first n characters.

firstN('hello', 3) // → 'hel'
firstN('abcdef', 4) // → 'abcd'

💡 Hints (1)