tl;dr: Generic Pattern Counter

// THIS IS WHAT YOU NEED

const count = (str) => {

  const re = /YOUR_PATTERN_HERE/g

  return ((str || '').match(re) || []).length

}

For those that arrived here looking for a generic way to count the number of occurrences of a regex pattern in a string, and don't want it to fail if there are zero occurrences, this code is what you need. Here's a demonstration:

/*

 *  Example

 */



const count = (str) => {

  const re = /[a-z]{3}/g

  return ((str || '').match(re) || []).length

}



const str1 = 'abc, def, ghi'

const str2 = 'ABC, DEF, GHI'



console.log(`'${str1}' has ${count(str1)} occurrences of pattern '/[a-z]{3}/g'`)

console.log(`'${str2}' has ${count(str2)} occurrences of pattern '/[a-z]{3}/g'`)

Original Answer

The problem with your initial code is that you are missing the global identifier:

>>> 'hi there how are you'.match(/s/g).length;

4

Without the g part of the regex it will only match the first occurrence and stop there.

Also note that your regex will count successive spaces twice:

>>> 'hi  there'.match(/s/g).length;

2

If that is not desirable, you could do this:

>>> 'hi  there'.match(/s+/g).length;

1