Chart.js/test/specs/core.element.tests.js

// Test the core element functionality
describe('Core element tests', function() {
	it ('should transition model properties', function() {
		var element = new Chart.Element({
			_model: {
				numberProp: 0,
				numberProp2: 100,
				_underscoreProp: 0,
				stringProp: 'abc',
				objectProp: {
					myObject: true
				},
				colorProp: 'rgb(0, 0, 0)'
			}
		});

		// First transition clones model into view
		element.transition(0.25);

		expect(element._view).toEqual(element._model);
		expect(element._view.objectProp).toBe(element._model.objectProp); // not cloned

		element._model.numberProp = 100;
		element._model.numberProp2 = 250;
		element._model._underscoreProp = 200;
		element._model.stringProp = 'def';
		element._model.newStringProp = 'newString';
		element._model.colorProp = 'rgb(255, 255, 0)';

		element.transition(0.25);

		expect(element._view).toEqual({
			numberProp: 25,
			numberProp2: 137.5,
			_underscoreProp: 0, // underscore props are not transition to a new value
			stringProp: 'def',
			newStringProp: 'newString',
			objectProp: {
				myObject: true
			},
			colorProp: 'rgb(64, 64, 0)',
		});
	});
});