Regular Expressions 101

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/
@(dog|cat)\b
/
g
@ matches the character @ with index 6410 (4016 or 1008) literally (case sensitive)
1st Capturing Group
(dog|cat)
1st Alternative
dog
dog
matches the characters dog literally (case sensitive)
2nd Alternative
cat
cat
matches the characters cat literally (case sensitive)
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
Global pattern flags
g modifier: global. All matches (don't return after first match)
Your regular expression does not match the subject string.Try launching the debugger to find out why.

Regular Expression
No Match

/
/
g

Test String