JavaScript inheritance extend function

Question

I\'m having some trouble understanding the IF clause at the end of this function from Pro JavaScript Design Patterns:

function extend(subClass, superClass) {         


        

Answer 1

The problem that those two lines try to avoid, is generally produced when you replace the prototype property of a Constructor Function, for example:

function Foo () {};
Foo.prototype = {
  bar: 'baz'
};

var foo = new Foo();
foo.constructor === Object; // true, but `constructor` should refer to Foo

When functions objects are created, the prototype property is initialized with a new object, which contains a constructor property that refers to the function itself, e.g.:

function Bar () {};
var bar = new Bar();
bar.constructor === Bar; // true

When you replace the prototype property with another object, this object has it's own constructor property, generally inherited from other constructor, or from Object.prototype.

var newObj = {};
newObj.constructor === Object;

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