fix(isLength): return true if min no supplied (#1070)

- ensure that even when user does not pass max and min, set defaults for the same
- instance, validator.isLength('aa') returns false, instead, we should return true and set min as 0 and max as undefined
- close #939

lib/isLength.js

@@ -22,7 +22,7 @@ function isLength(str, options) {
     max = options.max;
   } else {
     // backwards compatibility: isLength(str, min [, max])
-    min = arguments[1];
+    min = arguments[1] || 0;
     max = arguments[2];
   }
 

src/lib/isLength.js

@@ -9,7 +9,7 @@ export default function isLength(str, options) {
     min = options.min || 0;
     max = options.max;
   } else { // backwards compatibility: isLength(str, min [, max])
-    min = arguments[1];
+    min = arguments[1] || 0;
     max = arguments[2];
   }
   const surrogatePairs = str.match(/[\uD800-\uDBFF][\uDC00-\uDFFF]/g) || [];

test/validators.js

@@ -2795,6 +2795,10 @@ describe('Validators', () => {
       valid: [''],
       invalid: ['a', 'ab'],
     });
+    test({
+      validator: 'isLength',
+      valid: ['a', '', 'asds'],
+    });
   });
 
   it('should validate strings by byte length', () => {

validator.js

@@ -1007,7 +1007,7 @@ function isLength(str, options) {
     max = options.max;
   } else {
     // backwards compatibility: isLength(str, min [, max])
-    min = arguments[1];
+    min = arguments[1] || 0;
     max = arguments[2];
   }