Variables and Object creation using prototypes

[nrlz]

Try to guess what happens if I run the following code in any modern
browser. Don't cheat! Guess before you try it out.
Will I get:

1) 1,2...a,b
2) a,b...a,b
3) null...null
4) 1,2,a,b...1,2,a,b

Here is the code:

function Group() {
}

Group.prototype = {
members: [],

addMember: function(m) {
this.members.push(m);
},

listMembers: function() {
return this.members.join(",");
}
};

var my1 = new Group();
my1.addMember(1);
my1.addMember(2);

var my2 = new Group();
my2.addMember("a");
my2.addMember("b");

alert(my1.listMembers() + "..." + my2.listMembers());

Cheers!
Nathar

[Michael Winter]

On 30/04/2006 12:33, nr**@hotmail.com wrote:

Try to guess what happens if I run the following code in any modern
browser. [...]
A "modern browser" doesn't matter. Any correct ECMAScript implementation
will do.
Will I get:

1) 1,2...a,b
2) a,b...a,b
3) null...null
4) 1,2,a,b...1,2,a,b
[snip]
Group.prototype = {
members: [],

addMember: function(m) {
this.members.push(m);
},

listMembers: function() {
return this.members.join(",");
}
};

The latter (4). The members array is a property of the prototype object,
not objects created via the Group constructor function. As each
resulting object will /share/ the properties of the prototype, any
properties added to it will accumulate and be accessible to all instances.

[snip]

Mike

--
Michael Winter
Prefix subject with [News] before replying by e-mail.

[Matt Kruse]

nr**@hotmail.com wrote:

function Group() {
}

function Group() {
this.members = [];
}

This might cause it to behave more like you'd expect. This way, the
'members' variable belongs to each instantiated Group object, rather than to
the shared prototype.

--
Matt Kruse
http://www.JavascriptToolbox.com
http://www.AjaxToolbox.com

[nrlz]

You answered (4) and you are correct! Well done!

Incidentally, this script does require a browser, because it uses the
"alert" function.

Cheer!
Nathar

Michael Winter wrote:

On 30/04/2006 12:33, nr**@hotmail.com wrote:

Try to guess what happens if I run the following code in any modern
browser. [...]
A "modern browser" doesn't matter. Any correct ECMAScript implementation
will do.

[snip]
The latter (4). The members array is a property of the prototype object,
not objects created via the Group constructor function. As each
resulting object will /share/ the properties of the prototype, any
properties added to it will accumulate and be accessible to all instances.

[snip]

Mike

--
Michael Winter
Prefix subject with [News] before replying by e-mail.

[nrlz]

You answered (4) and you are correct! Well done!

Incidentally, this script does require a browser, because it uses the
"alert" function.

Cheer!
Nathar

Michael Winter wrote:

On 30/04/2006 12:33, nr**@hotmail.com wrote:

Try to guess what happens if I run the following code in any modern
browser. [...]

A "modern browser" doesn't matter. Any correct ECMAScript implementation
will do.

Will I get:

1) 1,2...a,b
2) a,b...a,b
3) null...null
4) 1,2,a,b...1,2,a,b

[snip]

Group.prototype = {
members: [],

addMember: function(m) {
this.members.push(m);
},

listMembers: function() {
return this.members.join(",");
}
};

The latter (4). The members array is a property of the prototype object,
not objects created via the Group constructor function. As each
resulting object will /share/ the properties of the prototype, any
properties added to it will accumulate and be accessible to all instances.

[snip]

Mike

--
Michael Winter
Prefix subject with [News] before replying by e-mail.

[Thomas 'PointedEars' Lahn]

nr**@hotmail.com wrote:

Try to guess what happens if I run the following code in any modern
browser. Don't cheat! Guess before you try it out.

Since when is this a quiz show? Get a life.
PointedEars
--
Multiple exclamation marks are a sure sign of a diseased mind.
-- Terry Pratchett

[Randy Webb]

Thomas 'PointedEars' Lahn said the following on 4/30/2006 5:04 PM:

nr**@hotmail.com wrote:

Try to guess what happens if I run the following code in any modern
browser. Don't cheat! Guess before you try it out.
Since when is this a quiz show?

Since when is it not? People ask questions, they may or may not get answers.
Get a life.

You first.

--
Randy
comp.lang.javascript FAQ - http://jibbering.com/faq & newsgroup weekly
Javascript Best Practices - http://www.JavascriptToolbox.com/bestpractices/