truncateString
Truncate a string if it is longer than the given maximum string length. Return the truncated string with a '...' ending.
Examples
truncateString('A-tisket a-tasket A green and yellow basket', 8) → 'A-tisket...'
truncateString('Peter Piper picked a peck of pickled peppers', 11) → 'Peter Piper...'
Starter code
function truncateString(str, num) {
}
Complexity of the optimal solution
Time O(k), space O(k). The `slice` method creates a new string of length `k` (where `k` is the `num` parameter). The time and space complexity are proportional to the length of the new truncated string, not the original string.