JavaScript Regular Expressions

Question 1

Which method tests whether a regular expression matches a string and returns a boolean?

Accepted Answer

regex.test(str)

Answer

The `test()` method on a RegExp object returns `true` if the pattern matches and `false` otherwise.

Question 2

What does the `g` flag do when added to a regular expression like `/abc/g`?

Accepted Answer

Finds all matches instead of stopping after the first

Answer

The `g` (global) flag causes methods like `match()` and `replace()` to process all occurrences in the string rather than just the first.

Question 3

Which character class shorthand matches any single digit (0–9)?

Accepted Answer

\d

Answer

`\d` is a shorthand character class equivalent to `[0-9]` and matches any single numeric digit.

Question 4

What does `^` mean when placed at the very start of a regex pattern (outside a character class)?

Accepted Answer

Asserts the match must start at the beginning of the string

Answer

Outside of a character class, `^` is an anchor that asserts the position is at the start of the string (or line in multiline mode).

Question 5

What does `String.prototype.replace(regex, newValue)` return when passed a regular expression?

Accepted Answer

A new string with the matched portion replaced

Answer

`replace()` returns a new string where matches of the regex are substituted with the replacement value; the original string is not mutated.

JavaScript Practice Test