How to count string occurrence in string?

Question

How can I count the number of times a particular string occurs in another string. For example, this is what I am trying to do in Javascript:

var temp = "This is a string.";
alert(temp.count("is")); //should output '2'

Answer 1

var temp = "This is a string.";

// the g in the regular expression says to search the whole string 
// rather than just find the first occurrence
var count = temp.match(/is/g);  

alert(count.length);

Answer 2

function countInstances(string, word) {
   var substrings = string.split(word);
   return substrings.length - 1;
}

Answer 3

You can use match to define such function:

String.prototype.count = function(search) {
    return this.match(new RegExp(search.toString().replace(/(?=[.\\+*?[^\]$(){}\|])/g, "\\"), "g")).length;
}

Answer 4

It depends on whether you accept overlapping instances, e.g.

var t = "sss";

How many instances of the substring "ss" are in the string above? 1 or 2? Do you leapfrog over each instance, or move the pointer character-by-character, looking for the substring?