JavaScript Regular Expressions 3

Question 1

What is a positive lookahead assertion in a regular expression?

Accepted Answer

A zero-width assertion that matches a position only if a specified pattern follows it

Answer

A positive lookahead `(?=...)` asserts that the enclosed pattern must follow the current position, without consuming characters in the match.

Question 2

What does `(?<=...)` represent in a JavaScript regular expression?

Accepted Answer

A positive lookbehind assertion that checks what precedes the current position

Answer

`(?<=...)` is a positive lookbehind; it matches a position only if the enclosed pattern appears immediately before it, without consuming those characters.

Question 3

What does the `s` (dotAll) flag do in a regular expression?

Accepted Answer

Allows `.` to match any character including newline (
)

Answer

By default, `.` does not match `
`; the `s` (dotAll) flag removes this restriction, making `.` match every character including newlines.

Question 4

Given a regex with a named capture group `(?<year>\d{4})`, how do you access the captured value from a `match()` result?

Accepted Answer

result.groups.year

Answer

Named capture groups are accessible via the `groups` property of the match result object, using the group name as the key.

Question 5

What does `str.split(/,\s*/)` do?

Accepted Answer

Splits the string on each comma, discarding any spaces that immediately follow it

Answer

The regex `/,\s*/` matches a comma followed by zero or more whitespace characters, so `split()` divides the string at those delimiters and trims leading spaces from each part.

JavaScript Practice Test

JavaScript Practice Test

JavaScript Regular Expressions 3