OperationSelector = function(selectElement) {
this.selectElement = selectElement;
}
OperationSelector.prototype.populateSelectWithData = function(xmlData) {
Assign it to a local variable in the function scope before your iteration function. Then you can reference it within:
OperationSelector = function(selectElement) {
this.selectElement = selectElement;
}
OperationSelector.prototype.populateSelectWithData = function(xmlData) {
var os = this;
$(xmlData).find('operation').each(function() {
var operation = $(this);
os.selectElement.append(new Option(operation.attr("title")));
});
}