Merge pull request #67 from jcsmesquita/master

Added ability to validate string with exact length.

src/locale.js

@@ -9,6 +9,7 @@ export let mixed = {
 
 export let string = {
   required:  '${path} is a required field',
+  length:    '${path} must be exactly ${length} characters',
   min:       '${path} must be at least ${min} characters',
   max:       '${path} must be at most ${max} characters',
   matches:   '${path} must match the following: "${regex}"',

src/string.js

@@ -45,6 +45,18 @@ inherits(StringSchema, MixedSchema, {
     )
   },
 
+  length(length, msg) {
+    return this.test({
+      name: 'length',
+      exclusive: true,
+      message:  msg || locale.length,
+      params: { length },
+      test(value) {
+        return isAbsent(value) || value.length === this.resolve(length)
+      }
+    })
+  },
+
   min(min, msg) {
     return this.test({
       name: 'min',

test/string.js

@@ -168,6 +168,26 @@ describe('String types', function(){
     ])
   })
 
+  it('should check LENGTH correctly', function(){
+    var v = string().length(5);
+    var obj = object({
+      len: number(),
+      name: string().length(ref('len'))
+    })
+
+    return Promise.all([
+      v.isValid('exact').should.eventually().equal(true),
+      v.isValid('sml').should.eventually().equal(false),
+      v.isValid('biiiig').should.eventually().equal(false),
+
+      v.isValid(null).should.eventually().equal(false),
+      v.nullable().isValid(null).should.eventually().equal(true),
+
+      obj.isValid({ len: 5, name: 'foo' }).should.eventually().equal(false)
+
+    ])
+  })
+
   it('should validate transforms', function(){
     return Promise.all([
       string().trim().isValid(' 3  ').should.eventually().equal(true),