Regular Expression to exclude a certain pattern

Question

I am trying to find the count of number of occurrences of a substring in a string using

function countOccurences(str,word){ var regex = new RegExp("\\b"+word+"\\b","gi"); console.log((str.match(regex)|| []).length); } let String=' test TEST TESTING Test I like testing <h3>TEST</h3> class="test id="test" '; let asset="Test"; countOccurences(String,asset);

Here, the result I am getting is 6, which is ok as I want the exact match, but I want to exclude the test of class and id, so that the result I get is 4 and not 6.

Wiktor Stribiżew · Accepted Answer · 2021-11-02 08:47:30Z

You can form a regex that will match and capture the substrings you would like to skip when counting and match the asset in other contexts only.

The sample regex may look like

/\b((?:id|class)="Test\b)|\bTest\b/gi

This will match

\b((?:id|class)="Test\b) - word boundary, Group 1 capturing id or class, then ="Test as a whole word
| - or
\bTest\b - whole word Test

See the JavaScript demo:

function countOccurences(str,exceptions,word){ const pattern = "\\b((?:" + exceptions.map(x => x.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&')).join("|") + ')="' + word + "\\b)|\\b"+word+"\\b"; const regex = new RegExp(pattern,"gi"); let count = 0, m; while (m = regex.exec(str)) { if (!m[1]) { count++; } } console.log(count) } let text = ' test TEST TESTING Test I like testing <h3>TEST</h3> class="test id="test" '; let asset="Test"; let exception_arr = ["id", "class"] countOccurences(text,exception_arr,asset); // => 4

Another solution is based on the negative lookarounds (not support in all JavaScript environments yet):

function countOccurences(str,exceptions,word){ const pattern = "\\b(?<!\\b(?:" + exceptions.map(x => x.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&')).join("|") + ')=")'+word+"\\b"; const regex = new RegExp(pattern,"gi"); console.log((str.match(regex) || ['']).length); } let text = ' test TEST TESTING Test I like testing <h3>TEST</h3> class="test id="test" '; let asset="Test"; let exception_arr = ["id", "class"] countOccurences(text,exception_arr,asset);

Here, /\b(?<!\b(?:id|class)=")Test\b/gi regex will match any Test as a whole word if it is not immediately preceded iwth id or class as whole words followed with =" substring.

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