`TextBlock().bind` missing type

[renancouto]

When using GoJS with Typescript the types provided for TextBlock().bind seem to be incomplete on the 2nd argument that is defined to accept only a string, while it also works with functions, like this:

new go.TextBlock().bind("text", (modelObj) => modelObj.prop)

This throws an error on the 2nd argument with the following message:

Argument of type '(modelObj: any) => any' is not assignable to parameter of type 'string'.ts(2345)

Would be nice to be able to use functions and also to have the model's object properties infered if possible.

[simonsarris]

The problem with that rests on determining what conditions would re-evaluate such a binding. The string is not just to define a source on the modelObj data, but to name the (typically, sole) property that needs to be observed for changes as well.

Normally writing:

new go.TextBlock().bind("text", "prop")

Will re-evaluate when "prop" is set (via model.set), and only re-evaluate then. And if you need a more complex binding than just observing "prop", you would write:

// An empty-string binding with a conversion function
new go.TextBlock().bind("text", "", (modelObj) => modelObj.prop)

Empty-string bindings are re-evaluated when any data on the model object changes, which are by this nature less efficient, so they are not something you'd want to use unless you had to.

I hope that makes sense. Is there some use case not covered here that I am missing?

[renancouto]

Hey, thanks a lot for the explanation! The empty string works fine.