Javascript RegEx partial match

Question

I have a regular expression pattern, which validates for a three digit number

/^\\d{3}$/.test(\"123\")   // true
/^\\d{3}$/.test(\"123.\")  // false
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Answer 1

You'll want to use explicit "|" partial matches. For your color matching example it's pretty simple, you just need to explicitly match an empty string partial

/^(|#[a-f0-9]{0,6})$/i.test(inputStr)

For an email it's more complicated since there are more partial match combinations

/^(|\w+|\w+@|\w+@\w+|\w+@\w+\.|\w+@\w+\.\w+)$/.test(inputStr)

Note that you can't get away with something like /^(|\w*@|...)$/ since that matches @blah.com which isn't a valid partial input.