Objects and Prototypal Inheritance - Test-Driven JavaScript Development - page 155

The test sets up a dummy object in the setUp method. It then asserts that
when extending an object, all the properties from the source object is copied over.
This method is definitely eligible for the Internet Explorer DontEnum bug, so
Listing 7.53 uses the tddjs.each method to loop the properties.

Listing 7.53 Initial implementation of tddjs.extend

tddjs.extend = (function () {
function extend(target, source) {
tddjs.each(source, function (prop, val) {
target[prop] = val;
});

}

return extend;
}());

The next step, seen in Listing 7.54, is to ensure that the two arguments are safe
to use. Any object will do on both sides; we simply need to make sure they're not
null or undefined .

Listing 7.54 Extending null

"test should return new object when source is null":
function () {
var object = tddjs.extend(null, this.dummy);

assertEquals("function", typeof object.getName);
assertEquals("function", typeof object.setName);

}

Note the expected return value. Listing 7.55 shows the implementation.

Listing 7.55 Allowing target to be null

function extend(target, source) {
target = target

|| {};

tddjs.each(source, function (prop, val) {
target[prop] = val;
});

return target;

}