CoffeeScript中的reduce（） - 如何传递默认值？

Question

So I've been toying around with CoffeeScript a bit recently. So far the transition from JS has been rather smooth, but now I've finally run into a problem I really can't figure out.

I've got this piece of ES6:

function upcaseOddIndexes (arr, cha, ind) {
  if (ind % 2 === 0) {
     arr.push(cha.toUpperCase());
  } else {
     arr.push(cha);
  }
  return arr;
}

var string = "stringthing";
var upcasedString = string.split("")
                    .reduce((arr, cha, ind) => upcaseOddIndexes (arr, cha, ind), [])
                    .join("");

console.log(upcasedArray);

which does its job (returning a new string with the letters at odd indexes uppercased) just fine. The upcaseOddIndexes function is no problem either. But how do I pass the empty array as the initialValue to reduce() ?

My best guess was

.reduce(arr, cha, ind -> upcaseOddIndexes arr, cha, ind) []

which gives me

.reduce(arr, cha, ind(function() {
  return upcaseOddIndexes(arr, cha, ind);
 }))([])

and that's going nowhere, since arr is not defined .

I've tried adding more parens, commas and whatnot, but I always meet with unexpected , or something similar.

I've already had a good rummage around Google, but haven't found an answer so far. There's this question on the topic, but it didn't really help.

Thanks a lot in advance =)

Answer 1

You can reduce (arr, cha, ind) => upcaseOddIndexes (arr, cha, ind) to upcaseOddIndexes :

string = "stringthing"
upcasedString = string
.split ""
.reduce upcaseOddIndexes, []
.join ""

That is converted to

var string, upcasedString;

string = "stringthing";

upcasedString = string.split("").reduce(upcaseOddIndexes, []).join("");

or without reduction:

string = "stringthing"
upcasedString = string
.split ""
.reduce (arr, cha, ind) ->
  upcaseOddIndexes arr, cha, ind
, []
.join ""

That is converted to

var string, upcasedString;

string = "stringthing";

upcasedString = string.split("").reduce(function(arr, cha, ind) {
  return upcaseOddIndexes(arr, cha, ind);
}, []).join("");

Answer 2

You need to specify the comma at the end of the call to reduce :

.reduce ((arr, cha, ind) ->
  upcaseOddIndexes arr, cha, ind
), []

You'll find a Javascript to Coffeescript converter here