1 files changed, 16 insertions, 0 deletions
diff --git a/ext/lib/ucs2length.js b/ext/lib/ucs2length.js
new file mode 100644
index 00000000..120a64d4
--- /dev/null
+++ b/ext/lib/ucs2length.js
@@ -0,0 +1,16 @@
+export default function ucs2length(str) {
+    const len = str.length;
+    let length = 0;
+    let pos = 0;
+    let value;
+    while (pos < len) {
+        length++;
+        value = str.charCodeAt(pos++);
+        if (value >= 0xd800 && value <= 0xdbff && pos < len) {
+            // high surrogate, and there is a next character
+            value = str.charCodeAt(pos);
+            if ((value & 0xfc00) === 0xdc00) pos++; // low surrogate
+        }
+    }
+    return length;
+}