What is the best method for counting the number of times a string appears within a string using JS?

For example:

count("fat math cat", "at") returns 3

What is the best method for counting the number of times a string appears within a string using JS?

For example:

count("fat math cat", "at") returns 3

• javascript
• string

6 Answers 6

Use a regex and then the number of matches can be found from the returned array. This is the naive approach using regex.

'fat cat'.match(/at/g).length

To protect against cases where the string doesn't match, use:

( 'fat cat'.match(/at/g) || [] ).length

Here:

function count( string, substring ) {
    var result = string.match( RegExp( '(' + substring + ')', 'g' ) ); 
    return result ? result.length : 0;
}

Don't use this, it's overplicated:

function count(sample, searchTerm) {
  if(sample == null || searchTerm == null) {
    return 0;
  }

  if(sample.indexOf(searchTerm) == -1) {
    return 0;
  }

  return count(sample.substring(sample.indexOf(searchTerm)+searchTerm.length), searchTerm)+1;
}

Can use indexOf in a loop:

function count(haystack, needle) {
    var count = 0;
    var idx = -1;
    haystack.indexOf(needle, idx + 1);
    while (idx != -1) {
        count++;
        idx = haystack.indexOf(needle, idx + 1);
    }
    return count;
}

function count(str,ma){
 var a = new RegExp(ma,'g'); // Create a RegExp that searches for the text ma globally
 return str.match(a).length; //Return the length of the array of matches
}

Then call it the way you did in your example. count('fat math cat','at');

You can use split also:

function getCount(str,d) {
    return str.split(d).length - 1;
}
getCount("fat math cat", "at"); // return 3