Formatação dentro de Javascript

<!DOCTYPE html>

<html>

<body>

<script>

var txt = "Olá Mundo!";

document.write("A cadeia de texto original: " + txt);

document.write("Big: " + txt.big() + "");

document.write("Small: " + txt.small() + "");

document.write("Bold: " + txt.bold() + "");

document.write("Italic: " + txt.italics() + "");

document.write("Fixed: " + txt.fixed() + "");

document.write("Strike: " + txt.strike() + "");

document.write("Fontcolor: " + txt.fontcolor("green") + "");

document.write("Fontsize: " + txt.fontsize(6) + "");

document.write("Subscript: " + txt.sub() + "");

document.write("Superscript: " + txt.sup() + "");

document.write("Link: " + txt.link("http://www.w3schools.com") + "");

document.write("Blink: " + txt.blink() + " (não funciona no IE, Chrome, Firefox ou Safari)");

</script>

</body>

</html>