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In Javascript is there a function that returns the number of times that a given string occurs?

Answer 1

+13 A:

T.J. Crowder 2010-03-24 14:59:00

instead of te can I pass a variable?

William Calleja 2010-03-24 15:04:44

@William: Sure, you can build a RegExp from a string: `new RegExp(theString, g)` (https://developer.mozilla.org/en/Core_JavaScript_1.5_Reference/Objects/RegExp), but you have to escape any special regex characters in the string (this is also true with the literal I supplied, but it's trickier in strings). For instance, to search for `[` you have to specify `\[` in a literal RegExp (`/\[/g`); to do that via a string you have to *further* escape the backslash since you're using it in a string literal, so: `new RegExp("\\[", g)`. You see how that can be more confusing. :-)

T.J. Crowder 2010-03-24 15:09:21

thanks a million sir, you're a life saver!

William Calleja 2010-03-24 15:12:52

@William: No worries. :-)

T.J. Crowder 2010-03-24 15:16:32

while (re.exec(str)) {}This is a lovely method, but it does not avoid creating arrays-it creates a new one each time you execute the loop.the match method you show first is a more efficient way to count pattern matches.

kennebec 2010-03-24 15:57:55

@kennebec: Very good point, my explanation was unclear. I meant that it avoided creating one large interim array. I've gone back and fixed that, thanks. :-)

T.J. Crowder 2010-03-24 16:31:43

@kennebec: And have now used `test` instead. Doh!

T.J. Crowder 2010-03-24 16:40:30

Answer 2

+2 A:

Here is an implementation of php's substr_count() in js. May this function bring you much joy...

substr_count = function(needle, haystack)
{
 var occurrences = 0;

 for (var i=0; i < haystack.length; i++)
 {
  if (needle == haystack.substr(i, needle.length))
  {
   occurrences++;
  }
 }

 return occurrences; 
}

alert(substr_count('hey', 'hey hey ehy w00lzworth'));

John Himmelman 2010-03-24 15:00:54

+1 for the argument names. :-)

T.J. Crowder 2010-03-24 15:17:14

Answer 3

+1 A:

I like to use test to count matches- with a global regular expression it works through a string from each lastIndex, like exec, but does not have to build any arrays:

var c=0;
while(rx.test(string)) c++


String.prototype.count= function(rx){
    if(typeof rx== 'string') rx= RegExp(rx,'g');
    var c= 0;
    while(rx.test(this)) c++;
    return c;
}

kennebec 2010-03-24 16:08:33

`RegExp#test` - doh! Big +1

T.J. Crowder 2010-03-24 16:40:47

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In Javascript is there a function that returns the number of times that a given string occurs?

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