string-convert-indexes^2.0.2

import { strict as assert } from "assert";
import {
  nativeToUnicode,
  unicodeToNative,
} from "string-convert-indexes";

// CONVERTING NATIVE JS INDEXES TO UNICODE-CHAR-COUNT-BASED
// 𝌆 - \uD834\uDF06

// at index 1, we have low surrogate, that's still grapheme index zero
assert.equal(
  nativeToUnicode("\uD834\uDF06aa", "1"),
  "0"
);
// notice it's retained as string. The same type as input is retained!

// at index 2, we have first letter a - that's second index, counting graphemes
assert.equal(nativeToUnicode("\uD834\uDF06aa", 3), 2);

// convert many indexes at once - any nested data structure is fine:
assert.deepEqual(
  nativeToUnicode("\uD834\uDF06aa", [1, 0, 2, 3]),
  [0, 0, 1, 2]
);

// numbers from an AST-like complex structure are still picked out and converted:
assert.deepEqual(
  nativeToUnicode("\uD834\uDF06aa", [
    1,
    "0",
    [[[2]]],
    3,
  ]),
  [
    0, // notice matching type is retained
    "0", // notice matching type is retained
    [[[1]]],
    2,
  ]
);

// CONVERTING UNICODE-CHAR-COUNT-BASED TO NATIVE JS INDEXES
// 𝌆 - \uD834\uDF06

assert.deepEqual(
  unicodeToNative("\uD834\uDF06aa", [0, 1, 2]),
  [0, 2, 3]
);

assert.deepEqual(
  unicodeToNative("\uD834\uDF06aa", [1, 0, 2]),
  [2, 0, 3]
);

assert.throws(() =>
  unicodeToNative("\uD834\uDF06aa", [1, 0, 2, 3])
);
// throws an error!
// that's because there's no character (counting Unicode characters) with index 3
// we have only three Unicode characters, so indexes go only up until 2