Untitled

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>JS Bin</title>
</head>
<body>

<script id="jsbin-javascript">
console.log( "Hola mundo".charAt(2) );
console.log( "Hola mundo"[2] );

let str = "Gato";

console.log(str[0]);
str[0] = 'Y';
console.log(str);
console.log(str[0]);
</script>


<script id="jsbin-source-javascript" type="text/javascript">console.log( "Hola mundo".charAt(2) );
console.log( "Hola mundo"[2] );

let str = "Gato";

console.log(str[0]);
str[0] = 'Y';
console.log(str);
console.log(str[0]);</script></body>
</html>