var persons = ["Gosling", "Bool", "Babbage", "Knuth", "Turing", "Lovelace"];

// will print index:personname
for (var i in persons) {
    if (window.console) {console.log(i  + ":" + persons[i]);}
}

// will print index:personname, and the original array (each time)
persons.forEach(function(entry, index, array) {
    if (window.console) {console.log(index + ":" + entry);}
    if (window.console) {console.log(array);}
});

// will print personname
for (var x of persons) {
    if (window.console) {console.log(x);}
}