amp-analytics: Shared interpolation & ampState() URL variable

[dreamofabear]

• Extract amp-analytics variable interpolation parsing (${var}) so it can be shared with another extension
• Implement ${ampState(foo.bar)} variable that reads from amp-bind state

/cc @lannka

[lannka]

The variable code is here

expandTemplate is the main function. Right now you can ignore any filter related code as they are dead code and @calebcordry is cleaning up.

To be clear, this VariableService code is to provide recursive var substitution to JSON config:

{
  vars: {
    varA: "123",
    varB: "${varA}"
  },

  requests: {
     a: "${varA}&${varB}"
  }
}

if you do expandTemplate(requests.a), it will return a promise of 123&123.

Another way to do similar thing is to use urlReplacementService, of which the code is already in core. To get what you want, you will add an AMP_STATE macro to url-replacements-impl.js, and use it like:

{
  requests: {
   a: "AMP_STATE(x)"
  }
}

I think urlReplacementService might be a better choice at this point, despite its name does not sound relevant.

[dreamofabear]

Thanks for the pointers Hongfei. Let's work with the requesting team and see if they can contribute this if possible.

[calebcordry]

I agree with Hongfei. If you want to point them at the specific place where the Macros are defined it is here. That is a simple one but others can get fairly complex.

I have been recently been spending a lot of time with this code so let me know if I can help.

[jamesshannon]

It looks like this is the FR to support amp-bind state variables in amp-analytics. If so, +1.

Use case: Ecommerce partner has a shopping cart and wants to set up an analytics ping for add-to-cart. That ping would include the product ID and price (which can be SSR'ed into the page) and also # of items being added.

One alternative way to implement this might be to allow data-vars-* to be bindable. E.g [data-vars-num-products]="cart[count]".

[dreamofabear]

@jamesshannon That's already done: https://github.com/ampproject/amphtml/blob/master/spec/amp-var-substitutions.md#amp-state

[ampprojectbot]

This issue hasn't been updated in awhile. Do you have any updates?

[zhouyx]

Is there any work left here?

[dreamofabear]

I believe sharing variable interpolation code between extensions is not done yet. I think priority can be dropped though.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 7 days if no further activity occurs. Thank you for your contributions.