Loose checking for calling JavaScript theme function

Problem/Motivation

JavaScript theme functions are defined on each library and Drupal.theme() checks property existence. But, a type of property value is not checked so that if a JavaScript theme function is defined other than function, tries to execute as function and occurs an error.

Drupal.theme.test = true;

Drupal.theme.test2 = function() {
	// Try to execute Drupal.theme.test() as a function but an error is occurred.
	return Drupal.theme('test', false);
}

Proposed resolution

Checks property value type using typeof operator.

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet