If you want to make your computed observable writable as well then you have to use purecomputed , it works as same but only differnce is here you get the access t write as well
chemistViewModel.chemist_mailingAddress = ko.pureComputed({
read: function () {
if (chemistViewModel.chemist_isMailingAddressReadOnly()) {
var updatedAddress = chemistViewModel.chemist_AddressLine1() + ' ' + chemistViewModel.chemist_AddressLine2() + ' ' + chemistViewModel.chemist_AddressLine3();
return updatedAddress;
}
else {
var updatedAddress = chemistViewModel.chemist_mailingAddressWritable();
return updatedAddress;
}
},
write: function (value) {
if (!chemistViewModel.chemist_isMailingAddressReadOnly()) {
chemistViewModel.chemist_mailingAddressWritable(value);
}
},
owner: this
});