amp-bind: Multiple args in closure functions e.g. reduce()

[tbaik]

What's the issue?

The Array.reduce function in an amp-bind expression currently only allows one parameter (the callback function) to be passed in. There should be support for the second parameter (initial value) as well.

One can prepend an initial value to an array before using the reduce function but having the second parameter is more ideal.

How do we reproduce the issue?

[1, 2, 3].reduce((x, y) => x + y) is OK.
[1, 2, 3].reduce((x, y) => x + y, 0) is not accepted.

What browsers are affected?

All browsers

Which AMP version is affected?

Latest.

CC: @jmarkoff & @sebastianbenz

[dreamofabear]

Agree that would be better. For prioritization: are there cases where a workaround doesn't exist?

[tbaik]

@choumx I have been able to get around this with the mentioned workaround for all of my cases so far! I imagine it works for all other cases as well.

[x0bandeira]

Hi there, I believe this along with operands limit on expressions, make it impossible or very hard to reduce into another array which is useful for state management of state/arrays.

[dreamofabear]

@COMMAND3R Do you have an example you can share?

[rizalpascual]

@choumx, Our use case needs this one to be fixed:
[1, 2, 3].reduce((x, y) => x + y, 0) is not accepted.

We use that approach to sum/total the items of our array.
e.g.

<span [text]="' $' + shoppingCart.items.map((item, index) => item.price).reduce((x, y) => x + y, 0)">

Is there a workaround to avoid the validation issue. Our use case needs the array to be empty initally.

Thanks.