javascript - how can I get a regex that allows only 0000 or spaces

Question

how can I get a regex that allows only 0000 or spaces, but not both

examples:

1. 0000000000000000000 --> OK;
2. only spaces --> OK;
3. 000000000 0000 --> Not Ok;
4. afads0000 00 0fd --> Not Ok;

Answer 1

^(?:0+| +)$

Explanation:

^      # Start of string
(?:    # Either match (but don't capture)...
 0+    # one or more zeroes
|      # or
 [ ]+  # one or more spaces
)      # End of non-capturing group (used to contain the alternation)
$      # End of string