JS/TS 函数到 Dart 函数

Question

I want to convert it to dart code but I dnt understand ternary operator in that code

const getPagination = (page, size) => {
  const limit = size ? +size : 3
  const from = page ? page * limit : 0
  const to = page ? from + size - 1 : size - 1

  return { from, to }
}

if you can tell me what code do line by line??

Answer 1

A more idiomatic Dart implementation of the same code could be:

Range getPagination([int page = 0, int size = 3]) {
  RangeError.checkNotNegative(page, "page");
  if (size <= 0) size = 3;
  var from = page * size;
  var to = from + size - 1;
  return Range(from, to);
}

class Range {
  final int from;
  final int to;
  Range(this.from, this.to);
}

This allows you to call with no arguments, but not with null as explicit argument. So don't do that.

If you omit the size, the size is 3 . That's more useful than finding a limit if size is null or 0 , but then use size anyway in the to computation, instead of limit .

Using a list of integers as a pair of integers is not the Dart way. I'd create a class, like here, or wait for records and use a proper (int, int) tuple.

Dart lists, and maps, are much more expensive data structures than JavaScript "objects". A small class is what corresponds to the anonymous object {from, to} in JavaScript.

Answer 2

so I convert it by looking at TS play code

void main() {
  List<int> getPagination(int? page, int? size) {
  int? limit = size ?? 3;
  int? from = page != null ? page * limit : 0;
  int? to = page != null ? (from + size!) - 1 : (size! - 1);

  return [from, to];
}
  print(getPagination(0, 10));
}

and its works thx to @blex