CODEWITHSUNDEEP
javascriptregexregular-language
Max_Salah
Max_Salah

Reputation: 2497

Pattern for DNF Function (javascript regular expression)

I would like to validate the DNF (Disjunctive normal form) which looks like this A*B+A'*C+C*D*E'. For this purpose, I use the folloing following pattern:

/[A-Z]'?(\*[A-Z]'?)*(\+[A-Z]'?(\*[A-Z]'?)*)+/g

I have tested this pattern using javascript test() method in this online tool: http://www.pagecolumn.com/tool/regtest.htm and it gives me the result I have expected.

I tried to test the pattern with javascript, using the following code:

  <script type="text/javascript">
    var dnf="A*3+A*B+CD";
    var pattern= /[A-Z]'?(\*[A-Z]'?)*(\+[A-Z]'?(\*[A-Z]'?)*)+/g;
    var flag = false;
    flag=pattern.test(dnf);
    console.log(flag);
  </script>

The problem is, I don't understand, why flag (in this code) become "true", which has to be "false" cause the terms A*3 and CD in the dnf="A*3+A*B+CD".

I have testet this in the online tester and it says: no matches, what I think is right.

Upvotes: 2

Views: 832

Answers (2)

Andrew Clark
Andrew Clark

Reputation: 208555

I think you must have entered this into the online tester incorrectly, because I tried the same thing and it is matching "A*B+C" from the string "A*3+A*B+CD":

enter image description here

If you only want to match if the entire string matches your pattern, add start and end of string anchors:

/^[A-Z]'?(\*[A-Z]'?)*(\+[A-Z]'?(\*[A-Z]'?)*)+$/g

Upvotes: 0

nrabinowitz
nrabinowitz

Reputation: 55678

You aren't specifying that the match has to begin at the beginning of the string or end at the end of it. So if a substring matches, the pattern test will return true. In this case, it looks like A*B+C (a substring of your original string) will match the pattern.

To fix, require that the whole string is matched, using ^ and $:

var pattern= /^[A-Z]'?(\*[A-Z]'?)*(\+[A-Z]'?(\*[A-Z]'?)*)+$/;

Note that the g flag no longer makes any sense in this context, as you can only have one match.

Upvotes: 1

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