How to check that custom property values are defined

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To enhance the data model, medini offers various types like string or date or custom scripted properties. On the user interface they are rendered nicely, but sometimes a script has to deal with those properties and its required to test for an existence of a value before the script can move on, this article quickly tackles what need to be considered.

Single String Property

If you have a single string value, its rather simple, you either get a string or you get "undefined" or "null". So to distinguish you simply can do:

if (self.user_single_property != undefined) {
 // TODO do something with the value
}

// be careful, this works as well
if (self.user_single_property) {
 // TODO do something with the value
}

// but is the same as
if (self.user_single_property != undefined && self.user_single_property != "") {
 // TODO do something with the value
} 

Multi-String Property

These values are always returned as a list. You can use isEmpty() on the list or size() == 0 to check if there is nothing set:

if (!self.user_multi_value.isEmpty()) {
 console.log("There are {0} values inside", self.user_multi_value.size());
 // TODO do something with the values in the list
}

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Single or Multi or Derived Property

If you have a situation in which the script does not know whether its a single or multi value property, or if you have a derived property that may return an arbitrary object, you may use these snippets:

if (self.user_prop && typeof self.user_prop == "string") {
 // OK, a single value string
} 

if (self.user_prop && "isEmpty" in self.user_prop && typeof self.user_prop["isEmpty"] == "function") {
 // OK, a multi value string
}