Add string.exactLength (#236)

README.md

@@ -266,6 +266,16 @@ UserSchema.validate({
     Nope.string()
       .lessThan(4)
       .validate('http'); // returns the error message
+
+  - `exactLength(length: number, message: string)` - Asserts if the entry is of exact length
+  - ```js
+    Nope.string()
+      .exactLength(4)
+      .validate('test'); // returns undefined
+
+    Nope.string()
+      .exactLength(4)
+      .validate('testing'); // returns the error message
     ```
 
 - `Number`

src/NopePrimitive.ts

@@ -54,6 +54,10 @@ abstract class NopePrimitive<T> implements Validatable<T> {
 
   public oneOf(options: (T | NopeReference | Nil)[], message = 'Invalid option') {
     const rule: Rule<T> = (entry, context) => {
+      if (entry === undefined) {
+        return;
+      }
+
       const resolvedOptions = options.map((option) => resolveNopeRef(option, context));
 
       if (resolvedOptions.indexOf(entry) === -1) {

src/NopeString.ts

@@ -110,6 +110,21 @@ class NopeString extends NopePrimitive<string> {
 
     return this.test(rule);
   }
+
+  public exactLength(length: number, message = `Must be at exactly of length ${length}`) {
+    const rule: Rule<string> = (entry) => {
+      if (this.isEmpty(entry)) {
+        return;
+      }
+
+      const value = entry as string;
+      if (value.length !== length) {
+        return message;
+      }
+    };
+
+    return this.test(rule);
+  }
 }
 
 export default NopeString;

src/__tests__/NopeString.spec.ts

@@ -186,4 +186,13 @@ describe('#NopeString', () => {
       expect(Nope.string().required('requiredMessage').validate('     ')).toBe('requiredMessage');
     });
   });
+
+  describe('#exactLength', () => {
+    it('should return work', () => {
+      expect(Nope.string().exactLength(5, 'msg').validate(undefined)).toBe(undefined);
+      expect(Nope.string().exactLength(5, 'msg').validate('123')).toBe('msg');
+      expect(Nope.string().exactLength(5, 'msg').validate('123456')).toBe('msg');
+      expect(Nope.string().exactLength(5, 'msg').validate('lucky')).toBe(undefined);
+    });
+  });
 });