js4py: core-javascript/core-javascript-work/tutorial.js comparison

comparison core-javascript/core-javascript-work/tutorial.js @ 141:e8bfe6c50a01 core-javascript

Add commentary to what-is-new.rst.

author	Jonathan Fine <jfine@pytex.org>
date	Mon, 31 Oct 2011 21:17:17 +0000
parents	abfb176c7346
children

comparison

equal deleted inserted replaced

-:abfb176c7346
+:e8bfe6c50a01
 // start new-operator
 TEST('new-operator', function()
 {
+// A 'traditional class'.  It records 'this' as a side effect.
 var this_in_Fn;
 var Fn = function(){
 this_in_Fn = this;
 };
-this_in_Fn = null;
+// Call the 'class' without the 'new'.
+this_in_Fn = null;          // Clear any previous value.
 var non_instance = Fn();
 assert( non_instance === undefined );
 assert( this_in_Fn.telltail === 'global');
-this_in_Fn = null;
+// Call the 'class' with the 'new'.
+this_in_Fn = null;          // Clear any previous value.
 var instance = new Fn();
 assert( instance === this_in_Fn );
 assert( instance.telltail === undefined );
+// Demonstrate that instance is a descendant of Fn.prototype.
 Fn.prototype.telltail = 'instance-of-Fn';
 assert( instance.telltail === 'instance-of-Fn' );
-Fn.prototype = {
+// We can give Fn a new prototype.
-telltail : 'prototype-is-changed'
+instance.new_telltail = 'child-of-instance';
-};
+Fn.prototype = instance;
+// And now an instance of Fn has two telltails.
 var second_instance = new Fn();
-assert( second_instance.telltail === 'prototype-is-changed' );
+assert( second_instance.telltail === 'instance-of-Fn' );
+assert( second_instance.new_telltail === 'child-of-instance' );
-Fn.prototype = second_instance;
-second_instance.i = 42;
-var third_instance = new Fn();
-assert( third_instance.telltail === 'prototype-is-changed' );
-assert( third_instance.i === 42 );
 });
 // end new-operator