Stringsのリファクタ

lib/strings.js

@@ -2,13 +2,17 @@
 
 const { getValidNumber } = require('./common');
 
+function getStringSegmentOf(text) {
+    const segmentation = new Intl.Segmenter('ja', { granularity: 'grapheme' });
+    return [...segmentation.segment(text)];
+}
+
 function stringLength(text) {
     if (typeof text !== 'string') {
         throw new Error('text is not string type.');
     }
 
-    const segmentation = new Intl.Segmenter('ja', { granularity: 'grapheme' });
-    return [...segmentation.segment(text)].length;
+    return getStringSegmentOf(text).length;
 }
 
 function getStartIndex(start, strLength) {
@@ -33,19 +37,14 @@ function stringSlice(text, start, end) {
     const startIndex = getStartIndex(start, strLength);
     const endIndex = getEndIndex(end, strLength);
 
-    let strings = '';
-
     if (startIndex >= strLength || endIndex <= startIndex) {
-        return strings;
+        return '';
     }
-    const segmentation = new Intl.Segmenter('ja', { granularity: 'grapheme' });
-    [...segmentation.segment(text)]
-        .forEach((value, index) => {
-            if (startIndex <= index && index < endIndex) {
-                strings += value.segment;
-            }
-        });
-    return strings;
+    return getStringSegmentOf(text)
+        .map((element, index) => {
+            return startIndex <= index && index < endIndex ? element.segment : '';
+        })
+        .join('');
 }
 
 module.exports = {