fix(isByteLength): handle unpaired surrogates instead of throwing

src/lib/isByteLength.js

@@ -12,6 +12,20 @@ export default function isByteLength(str, options) {
     min = arguments[1];
     max = arguments[2];
   }
-  const len = encodeURI(str).split(/%..|./).length - 1;
+  // encodeURI() throws on unpaired surrogates, so replace any with U+FFFD first.
+  // A UTF-8 encoder substitutes the same replacement character (3 bytes), which
+  // keeps the byte count correct while leaving valid surrogate pairs untouched.
+  const sanitized = str.replace(/[\uD800-\uDFFF]/g, (surrogate, index) => {
+    const isHighSurrogate = surrogate.charCodeAt(0) <= 0xDBFF;
+    if (isHighSurrogate) {
+      const next = str.charCodeAt(index + 1);
+      if (next >= 0xDC00 && next <= 0xDFFF) return surrogate;
+    } else {
+      const prev = str.charCodeAt(index - 1);
+      if (prev >= 0xD800 && prev <= 0xDBFF) return surrogate;
+    }
+    return '\uFFFD';
+  });
+  const len = encodeURI(sanitized).split(/%..|./).length - 1;
   return len >= min && (typeof max === 'undefined' || len <= max);
 }

test/validators.test.js

@@ -5757,6 +5757,22 @@ describe('Validators', () => {
     });
   });
 
+  it('should not throw on unpaired surrogates', () => {
+    // encodeURI() throws a URIError on unpaired surrogates; isByteLength must
+    // count them (as the U+FFFD replacement character, 3 bytes) rather than crash.
+    test({
+      validator: 'isByteLength',
+      args: [{ min: 0, max: 3 }],
+      valid: ['\uD835', '\uDC00', '\uDFFF'],
+      invalid: ['\uD835\uDB00'],
+    });
+    // isEmail() runs the local part through isByteLength, so it inherited the crash.
+    test({
+      validator: 'isEmail',
+      invalid: ['\uD835', 'foo\uD835@bar.com'],
+    });
+  });
+
   it('should validate ULIDs', () => {
     test({
       validator: 'isULID',