Edit in JSFiddle

var myString= "A word character is 0123456789, ABCDEFGHIGKLMNOPQRSTUVWXYZ, abcdefghijklmnopqrstuvwxyz, and _";

var search = myString.search(/_/g);

console.log(search); //logs 92

console.log(myString.length - 1); //logs 92, subtract 1 to get zero based index