check if string has letter js code example

Example 1: javascript contains substring

var str = "We got a poop cleanup on isle 4.";
if(str.indexOf("poop") !== -1){
	alert("Not again");
}
//use indexOf (it returns position of substring or -1 if not found)

Example 2: check if something is a letter in js

string.charAt(1).toUpperCase() !== string.charAt(1).toLowerCase()