website out of date - incorrect arguments to attributeChanged method

[BugsNash]

In the life cycle methods section of the API reference page, the attributeChanged method is demonstrated with incorrect arguments

attributeChanged: function(attrName, oldVal, newVal) {
//var newVal = this.getAttribute(attrName);
console.log(attrName, 'old: ' + oldVal, 'new:', newVal);
},

In practice, the first argument to this function is oldVal, the second is newVal.

http://www.polymer-project.org/polymer.html#lifecyclemethods

[sjmiles]

Afaict, the spec, the polyfill, Polymer source code, and http://jsbin.com/ixIpIMa/5/edit all agree on the call signature.

Do you have a reproduction you can share?

[BugsNash]

I do, I'll grab it now and send it in a sec. Even later in the same page it
says that the call signature is function(oldValue, newValue):

http://www.polymer-project.org/polymer.html#observeprops

Bugs

On Thu, Feb 13, 2014 at 11:12 AM, Scott J. Miles
[email protected]:

Afaict, the spec, the polyfill, Polymer source code, and
http://jsbin.com/ixIpIMa/5/edit all agree on the call signature.

Do you have a reproduction you can share?

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/419#issuecomment-34934584
.

[sjmiles]

Ah, attribute confusion.

For any observed property, we support a magic method called <property>Changed. If I observe foo then I can make a fooChanged that will be called when the value of foo changes.

This is not to be confused with attributeChanged which is a special method that is called when any attribute is modified on the element.

If you made a property called attribute that could explain the confusion.

[BugsNash]

aaaaaah ok so attributeChanged is the literal name of a function that is
called whenever any attribute is changed, and Changed is a specialised
method that is called only when property x is changed. I assume this means
that when x xhanges both xChanged and attributeChanged are called?

Bugs

On Thu, Feb 13, 2014 at 11:41 AM, Scott J. Miles
[email protected]:

Ah, attribute confusion.

For any observed property, we support a magic method called
Changed. If I observe foo then I can make a fooChanged that
will be called when the value of foo changes.

This is not to be confused with attributeChanged which is a special
method that is called when any attribute is modified on the element.

If you made a property called attribute that could explain the confusion.

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/419#issuecomment-34936442
.

[sjmiles]

Yes, sorry for the confusion.

It's best to just consider that attributeChanged is called when an attribute changes, and <property>Changed is called when <property> changes.

It's true that properties are sometimes tied to attributes, but not always. Whether a change in a property results in a change in an attribute isn't as obvious as it seems.

The short version is that Polymer tries to be smart about doing the least amount of work it can while keeping your logic correct.

[BugsNash]

Excellent thanks for the explanation!

Bugs

On Thu, Feb 13, 2014 at 12:00 PM, Scott J. Miles
[email protected]:

Yes, sorry for the confusion.

It's best to just consider that attributeChanged is called when an
attribute changes, and Changed is called when changes.

It's true that properties are sometimes tied to attributes, but not
always. Whether a change in a property results in a change in an attribute
isn't as obvious as it seems.

The short version is that Polymer tries to be smart about doing the least
amount of work it can while keeping your logic correct.

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/419#issuecomment-34937665
.