JavaScript access string chars as array

Using charAt is probably the best idea since it conveys the intent of your code most accurately. Calling substr for a single character is definitely an overkill.

alert(myString.charAt(0));

Accessing characters as numeric properties of a string is non-standard prior to ECMAScript 5 and doesn't work in all browsers (for example, it doesn't work in IE 6 or 7). You should use myString.charAt(0) instead when your code has to work in non-ECMAScript 5 environments. Alternatively, if you're going to be accessing a lot of characters in the string then you can turn a string into an array of characters using its split() method:

var myString = "Hello!";
var strChars = myString.split("");
alert(strChars[0]);