selection.data

[daenenk]

The current implementation requires a Function3 as key function.

def data[NewDatum](data: js.Array[NewDatum], key:js.Function3[NewDatum, Int, Int, String]): Update[NewDatum] = js.native

This implementation gives execution errors when running with d3.js (master 20 May 2015 > tag 3.5.9)
complaining that the 3 argument is undefined iso Int.

The d3.js documentation only describes a function with one or two arguments: datum and index.

This can be corrected :

def data[NewDatum](data: js.Array[NewDatum], key: js.Function2[NewDatum, Int, String]): Update[NewDatum] = js.native

[spaced]

Its even more complicated:
The key function is called twice during the data binding process, which proceeds in two phases.
key function must be a js.ThisFunction2[Datum|NewDatum,js.UndefOr[NewDatum], Int, String]
In first loop d is undefined, this is Datum
In second loop d is NewDatum and this is also NewDatum
See also http://stackoverflow.com/questions/27577368/d3-js-key-function-running-twice-on-simple-selector-array-combo

[spaced]

Please reopen if you are not happy with the solution.

[daenenk]

Indeed, it is more complex than I initially thought. Have a look to the example I posted on the force layout Issue; it is related.
Would it make sense to bound the NewDatum?

def data[NewDatum <: Datum]( ...