sassIndexToRuneIndex method

int sassIndexToRuneIndex(
  1. Value sassIndex,
  2. [String? name]

Converts sassIndex into a Dart-style index into text.runes.

Sass indexes are one-based, while Dart indexes are zero-based. Sass indexes may also be negative in order to index from the end of the string.

See also sassIndexToStringIndex, which an index into text directly.

Throws a SassScriptException if sassIndex isn't a number, if that number isn't an integer, or if that integer isn't a valid index for this string. If sassIndex came from a function argument, name is the argument name (without the $). It's used for error reporting.


int sassIndexToRuneIndex(Value sassIndex, [String? name]) {
  var index = sassIndex.assertNumber(name).assertInt(name);
  if (index == 0) {
    throw SassScriptException("String index may not be 0.", name);
  } else if (index.abs() > sassLength) {
    throw SassScriptException(
        "Invalid index $sassIndex for a string with $sassLength characters.",

  return index < 0 ? sassLength + index : index - 1;