1var temp = "This is a string.";
2var count = (temp.match(/is/g) || []).length;
3console.log(count);
4
5Output: 2
6
7Explaination : The g in the regular expression (short for global) says to search the whole string rather than just find the first occurrence. This matches 'is' twice.

1var str = "Hello World!";
2var n = str.length;