Added isFieldValid method to Validation

Author: bondom

README.md

@@ -228,7 +228,11 @@ this.setState(
 Use this method inside the render function, like in the [example](#form-example). It will return the object with fields keys and their error messages. If the field is valid there will be an empty error string.
 
 ### isFormValid({state})
-Use this method to check, if the field is valid. It will return true, if all the fields in the form are valid. See the [example](#form-example)
+Use this method to check, if the form is valid. It will return true, if all the fields in the form are valid. See the [example](#form-example)
+
+### isFieldValid({state}, fieldName)
+Use this method to check, if particular field is valid. Returns true if it is valid, false otherwise
+
 
 ## Compatibility 
 This package id fully compatible with the React v.16, because it uses state updater functions inside.

__tests__/index.test.js

@@ -190,5 +190,27 @@ describe('Unit tests for Validation class', () => {
       state = Object.assign({}, state, result);
       expect(Validator.isFormValid(state)).toEqual(true);
     });
+
+    test('Validator.isFieldValid(state,"login") method returns false', () => {
+      const updater = Validator.validate({
+        login: ''
+      });
+      const result = updater(state);
+      state = Object.assign({}, state, result);
+      expect(Validator.isFieldValid(state, 'login')).toEqual(false);
+    });
+
+    test('Validator.isFieldValid(state,"password") method returns true', () => {
+      expect(Validator.isFieldValid(state, 'password')).toEqual(true);
+    });
+
+    test('Validator.isFieldValid(state,"login") method returns true after login field became validated', () => {
+      const updater = Validator.validate({
+        login: 'peterson'
+      });
+      const result = updater(state);
+      state = Object.assign({}, state, result);
+      expect(Validator.isFieldValid(state, 'login')).toEqual(true);
+    });
   });
 });

src/index.js

@@ -37,6 +37,7 @@ class Validation {
   storage: string;
   statuses: Array<string>;
 
+  // TODO: errorsStorageName is misleading, storage contains fields mapped to statuses but not errors
   constructor(
     fields: FieldsDescription,
     errorsStorageName: string = 'validationStorage'
@@ -202,15 +203,15 @@ class Validation {
   }
 
   isFormValid(state: Object): boolean {
-    const errors = state[this.storage];
-    if (typeof errors !== 'object') {
-      throw new Error('Invalid errors parameter for fields, must be object');
+    const fieldsMappedToStatuses = state[this.storage];
+    if (typeof fieldsMappedToStatuses !== 'object') {
+      throw new Error('Invalid fieldsMappedToStatuses object, must be object');
     }
 
-    const keys = Object.keys(errors);
+    const keys = Object.keys(fieldsMappedToStatuses);
     const [validationPassed] = this.statuses;
     for (let i = 0; i < keys.length; i++) {
-      const currentStatuses = errors[keys[i]];
+      const currentStatuses = fieldsMappedToStatuses[keys[i]];
       for (let j = 0; j < currentStatuses.length; j++) {
         if (currentStatuses[j] !== validationPassed) {
           return false;
@@ -220,6 +221,25 @@ class Validation {
     // if form valid return true
     return true;
   }
+
+  isFieldValid(state: Object, fieldName: string): boolean {
+    const fieldsMappedToStatuses = state[this.storage];
+    if (typeof fieldsMappedToStatuses !== 'object') {
+      throw new Error('Invalid fieldsMappedToStatuses object, must be object');
+    }
+    const fieldStatuses = fieldsMappedToStatuses[fieldName];
+    if (!fieldStatuses) {
+      throw new Error("Attempt to validate field that doesn't exist");
+    }
+
+    const [validationPassed] = this.statuses;
+    for (let j = 0; j < fieldStatuses.length; j++) {
+      if (fieldStatuses[j] !== validationPassed) {
+        return false;
+      }
+    }
+    return true;
+  }
 }
 
 const allRulesInArrays = (