I assume they mean to call the function from two (or more) parts of the code (i.e locations). It's not immediately apparent why this is meaningfully different than what would be possible in Java though, since ostensibly a function is the same as a method by just moving the callee to the list of parameters. (There are some things in a Java method that you can do that don't translate to most functional languages, like invoking the version of the method from a superclass, but there's nothing forcing you to do any of those from the language perspective, so it seems a bit strange to claim that the language itself is the issue rather than maybe the specific patterns that were chosen, maybe by their coworkers or just not common in the ecosystem).

I read it as „calling it from two places“

I read it as if your function contains a lot and you'd like to reuse part of this functionality in another place you don't have to figure it out how to abstract this. It's easy to just split your function in two parts and call the part you are interested in far away as is.

But I'm probably overthinking it.

I assume to split the overall behaviour (loop through all elements, transform some value, etc) and the specific one (apply this function to all elements, transform it in this way, etc) into multiple functions and combine those to achieve the actual intended behaviour.

At least that's my interpretation

Calling a function from two locations is what I meant.

Basically since moving to a functional approach in typescript I find I do not fight abstractions as I used to when I used classes and inheritance.

apparently it is not what the author meant but:

using projection you can "call a function in two parts"

  add: {x+y}
  add4: add[4] / gives {4+x} by fixing 4 as first argument to {x+y}
  add4[2]      / gives 6

this is a useful pattern that you can use to first 'fix' data or behaviour to produce another function

https://en.wikipedia.org/wiki/Partial_application

I believe they’re referring to callbacks / dependency injection / higher order functions to customize the behavior of a function?