2 files changed, 75 insertions, 40 deletions
diff --git a/ext/js/data/sandbox/string-util.js b/ext/js/data/sandbox/string-util.js
new file mode 100644
index 00000000..65d73eef
--- /dev/null
+++ b/ext/js/data/sandbox/string-util.js
@@ -0,0 +1,69 @@
+/*
+ * Copyright (C) 2022  Yomichan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/**
+ * Class containing generic string utility functions.
+ */
+class StringUtil {
+    /**
+     * Reads code points from a string in the forward direction.
+     * @param {string} text The text to read the code points from.
+     * @param {number} position The index of the first character to read.
+     * @param {number} count The number of code points to read.
+     * @returns {string} The code points from the string.
+     */
+    static readCodePointsForward(text, position, count) {
+        let result = '';
+        for (; count > 0; --count) {
+            const char = text[position];
+            const charCode = char.charCodeAt(0);
+            result += char;
+            if (charCode >= 0xd800 && charCode < 0xdc00 && ++position < text.length) {
+                const char2 = text[position];
+                const charCode2 = char2.charCodeAt(0);
+                if (charCode2 >= 0xdc00 && charCode2 < 0xe000) {
+                    result += char2;
+                }
+            }
+        }
+        return result;
+    }
+
+    /**
+     * Reads code points from a string in the backward direction.
+     * @param {string} text The text to read the code points from.
+     * @param {number} position The index of the first character to read.
+     * @param {number} count The number of code points to read.
+     * @returns {string} The code points from the string.
+     */
+    static readCodePointsBackward(text, position, count) {
+        let result = '';
+        for (; count > 0; --count) {
+            const char = text[position];
+            const charCode = char.charCodeAt(0);
+            result = char + result;
+            if (charCode >= 0xdc00 && charCode < 0xe000 && position > 0) {
+                const char2 = text[position - 1];
+                const charCode2 = char2.charCodeAt(0);
+                if (charCode2 >= 0xd800 && charCode2 < 0xdc00) {
+                    result = char2 + result;
+                }
+            }
+        }
+        return result;
+    }
+}
diff --git a/ext/js/dom/dom-text-scanner.js b/ext/js/dom/dom-text-scanner.js
index 7bed94a9..20aec9af 100644
--- a/ext/js/dom/dom-text-scanner.js
+++ b/ext/js/dom/dom-text-scanner.js
@@ -15,6 +15,10 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+/* global
+ * StringUtil
+ */
+
 /**
  * A class used to scan text in a document.
  */
@@ -146,44 +150,6 @@ class DOMTextScanner {
     // Private
 
     /**
-     * Reads a code point in a string in the forward direction.
-     * @param {string} text The text to read the code point from.
-     * @param {number} position The index of the first character to read.
-     * @returns {string} The code point from the string.
-     */
-    _readCodePointForward(text, position) {
-        let char = text[position];
-        const charCode = char.charCodeAt(0);
-        if (charCode >= 0xd800 && charCode < 0xdc00 && ++position < text.length) {
-            const char2 = text[position];
-            const charCode2 = char2.charCodeAt(0);
-            if (charCode2 >= 0xdc00 && charCode2 < 0xe000) {
-                char += char2;
-            }
-        }
-        return char;
-    }
-
-    /**
-     * Reads a code point in a string in the backward direction.
-     * @param {string} text The text to read the code point from.
-     * @param {number} position The index of the first character to read.
-     * @returns {string} The code point from the string.
-     */
-    _readCodePointBackward(text, position) {
-        let char = text[position];
-        const charCode = char.charCodeAt(0);
-        if (charCode >= 0xdc00 && charCode < 0xe000 && position > 0) {
-            const char2 = text[position - 1];
-            const charCode2 = char2.charCodeAt(0);
-            if (charCode2 >= 0xd800 && charCode2 < 0xdc00) {
-                char = char2 + char;
-            }
-        }
-        return char;
-    }
-
-    /**
      * Seeks forward in a text node.
      * @param {Text} textNode The text node to use.
      * @param {boolean} resetOffset Whether or not the text offset should be reset.
@@ -202,7 +168,7 @@ class DOMTextScanner {
         let newlines = this._newlines;
 
         while (offset < nodeValueLength) {
-            const char = this._readCodePointForward(nodeValue, offset);
+            const char = StringUtil.readCodePointsForward(nodeValue, offset, 1);
             offset += char.length;
             const charAttributes = DOMTextScanner.getCharacterAttributes(char, preserveNewlines, preserveWhitespace);
 
@@ -288,7 +254,7 @@ class DOMTextScanner {
         let newlines = this._newlines;
 
         while (offset > 0) {
-            const char = this._readCodePointBackward(nodeValue, offset - 1);
+            const char = StringUtil.readCodePointsBackward(nodeValue, offset - 1, 1);
             offset -= char.length;
             const charAttributes = DOMTextScanner.getCharacterAttributes(char, preserveNewlines, preserveWhitespace);