Show string diff before / after style #nodejs

index.js

import "colors";

import * as Diff from "diff";

const one = "こんにちは、きょうはいい天気ですね。";
const other = "こんばんは。今日は良い天気だね。";

const diff = Diff.diffChars(one, other);

function log(word) {
  process.stderr.write(word);
}

function showDiffedString(diff, word, fn) {
  let index = 0;
  let current = word.slice(index);

  for (const part of diff) {
    if (current.length === 0) {
      break;
    }

    if (current.startsWith(part.value)) {
      fn(part);
      current = current.slice(part.value.length);
    }
  }
}

log("Before: ");
showDiffedString(diff, one, (part) => {
  if (part.removed) {
    log(part.value["red"]);
  } else {
    log(part.value["grey"]);
  }
});
console.log();

log("After:  ");
showDiffedString(diff, other, (part) => {
  if (part.added) {
    log(part.value["green"]);
  } else {
    log(part.value["grey"]);
  }
});
console.log();

package.json

{
  "name": "tmp",
  "type": "module",
  "dependencies": {
    "colors": "^1.4.0",
    "diff": "^5.0.0"
  }
}