registerFunction method
Registers the key
as function name with the registry to be used in
function bindings. Functions registered by the application take
precidence over built in registered functions. This allows the
application the ability to provide custom functions even for built in
key
's.
Implementation
void registerFunction(
String key,
JsonWidgetFunction fun,
) {
assert(key.isNotEmpty == true);
_functions[key] = fun;
}