overhead of polymer-element bind data change monitoring

[Just.A.Guy]

I don't know how polymer does data binding.

I suspect it is using some time of "onChange" listener.

The more elements that there are to bind increases the overhead of supporting the two-way sync process.

I am wondering if there is not some waste in all that monitoring. In my experience there are two types

of data values.  

a. Constant - these are set at the time of the instance instantiation and do not change during the remaining time of execution.

b. non-constant - these change when the end user interacts with the application.

It seems that polymer only provides support for the type-b variables.  Yet because of that, as the number of variables

increases, performance can suffer.  If there was a way to identify type-a (constants), and then only bind those values

once (after ready?) without change monitoring, then the amount of monitoring for change may have a smaller impact.

Or maybe there is a type-c variable which is only changed by some javascript in a callback routine. Then provide

a function that re-values those changed variables.  And have the callback script call it after it makes a change.

That way the only monitored variables would be those that the end user can change. 

 

[Rafael Weinstein]

Polymer databinding supports one-time binding. Unfortunatey, this isn't documented yet (just opened this bug: https://github.com/Polymer/docs/issues/282), but the basic behavior is:

-any place you would use a double-mustache {{ foo }} to create a dynamic binding, you can use double brackets [[ foo ]] to create a one-time binding. This will not incur the overhead of setting up an observer.

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[Eric Bidelman]

Forgot to close that issue. We have docs here:

http://www.polymer-project.org/docs/polymer/expressions.html#single-use-bindings

Although, "Expressions" seems like the wrong page for this. Admittedly, all of the data-binding docs need a large overhaul :\

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