src/common/util.js/splitText
function splitText(text) {
  const KIND_NON_CJK = "non-cjk";
  const KIND_CJK_CHARACTER = "cjk-character";
  const KIND_CJK_PUNCTUATION = "cjk-punctuation";

  const nodes = [];

  text
    .replace(new RegExp(`(${cjkPattern})\n(${cjkPattern})`, "g"), "$1$2")
    .split(/([ \t\n]+)/)
    .forEach((token, index, tokens) => {
      // whitespace
      if (index % 2 === 1) {
        nodes.push({
          type: "whitespace",
          value: /\n/.test(token) ? "\n" : " "
        });
        return;
      }

      // word separated by whitespace

      if ((index === 0 || index === tokens.length - 1) && token === "") {
        return;
      }

      token
        .split(new RegExp(`(${cjkPattern})`))
        .forEach((innerToken, innerIndex, innerTokens) => {
          if (
            (innerIndex === 0 || innerIndex === innerTokens.length - 1) &&
            innerToken === ""
          ) {
            return;
          }

          // non-CJK word
          if (innerIndex % 2 === 0) {
            if (innerToken !== "") {
              appendNode({
                type: "word",
                value: innerToken,
                kind: KIND_NON_CJK,
                hasLeadingPunctuation: punctuationRegex.test(innerToken[0]),
                hasTrailingPunctuation: punctuationRegex.test(
                  getLast(innerToken)
                )
              });
            }
            return;
          }

          // CJK character
          appendNode(
            punctuationRegex.test(innerToken)
              ? {
                  type: "word",
                  value: innerToken,
                  kind: KIND_CJK_PUNCTUATION,
                  hasLeadingPunctuation: true,
                  hasTrailingPunctuation: true
                }
              : {
                  type: "word",
                  value: innerToken,
                  kind: KIND_CJK_CHARACTER,
                  hasLeadingPunctuation: false,
                  hasTrailingPunctuation: false
                }
          );
        });
    });

  return nodes;

  function appendNode(node) {
    const lastNode = getLast(nodes);
    if (lastNode && lastNode.type === "word") {
      if (
        (lastNode.kind === KIND_NON_CJK &&
          node.kind === KIND_CJK_CHARACTER &&
          !lastNode.hasTrailingPunctuation) ||
        (lastNode.kind === KIND_CJK_CHARACTER &&
          node.kind === KIND_NON_CJK &&
          !node.hasLeadingPunctuation)
      ) {
        nodes.push({ type: "whitespace", value: " " });
      } else if (
        !isBetween(KIND_NON_CJK, KIND_CJK_PUNCTUATION) &&
        // disallow leading/trailing full-width whitespace
        ![lastNode.value, node.value].some(value => /\u3000/.test(value))
      ) {
        nodes.push({ type: "whitespace", value: "" });
      }
    }
    nodes.push(node);

    function isBetween(kind1, kind2) {
      return (
        (lastNode.kind === kind1 && node.kind === kind2) ||
        (lastNode.kind === kind2 && node.kind === kind1)
      );
    }
  }
}