Count in String and Object

How
to count string occurrence in string?

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) || []).length;

alert(count);

http://stackoverflow.com/a/4009768/2177408

/** Function count the occurrences of substring in a string;
* @param {String} string   Required. The string;
* @param {String} subString    Required. The string to search for;
* @param {Boolean} allowOverlapping    Optional. Default: false;
* @author Vitim.us http://stackoverflow.com/questions/4009756/how-to-count-string-occurrence-in-string/7924240#7924240 */
function occurrences(string, subString, allowOverlapping) {

string += "";
subString += "";
if (subString.length <= 0) return (string.length + 1);

var n = 0,
pos = 0,
step = allowOverlapping ? 1 : subString.length;

while (true) {
pos = string.indexOf(subString, pos);
if (pos >= 0) {
++n;
pos += step;
} else break;
}
return n;
}

Usage

occurrences("foofoofoo", "bar"); //0

occurrences("foofoofoo", "foo"); //3

occurrences("foofoofoo", "foofoo"); //1

allowOverlapping

occurrences("foofoofoo", "foofoo", true); //2

Matches:

foofoofoo
1 '----'
2    '----'

http://stackoverflow.com/a/7924240/2177408

How
to efficiently count the number of keys/properties of an object in JavaScript?

What's the fastest way to count the number of keys/properties of an object? It it possible to do this without iterating over the object? i.e. without doing

var count = 0;
for (k in myobj) if (myobj.hasOwnProperty(k)) count++;

http://stackoverflow.com/q/126100/2177408
To do this in any ES5-compatible environment, such as Node, Chrome, IE 9+, FF 4+, or Safari 5+:

Object.keys(obj).length

Browser compatibility
Object.keys
documentation

(includes a method you can add to non-ECMA5 browsers)
http://stackoverflow.com/a/4889658/2177408