No 'for' Loop

Never again use 'for' for looping. Using 'for' can be dangerous, especially if you also use the library that add attributes to the native objects, such as the prototype library. If you use jQuery, do loops with $.each(). Change this loop
for (i in my_array_or_object) {
    if (my_checking_function(my_array_or_object[i])) {
        break;
    }
}
or
for (i = 0; i < my_array.length; ++i) {
    if (my_checking_function(my_array[i])) {
        break;
    }
}
to
$.each(my_array_or_object, function(i, value) {
    if (my_checking_function(value)) {
        return false;
    }
    return true;
});
If the circumtances force you to use 'for', do it this way
for (i in my_object) {
    if (!my_object.hasOwnProperty(i)) {
        continue;
    }
    if (my_checking_function(my_object[i])) {
        break;
    }
}