Added required fields support

Author: delvedor

example.js

@@ -16,7 +16,8 @@ const stringify = fastJson({
       type: 'integer'
     },
     now: {
-      type: 'string'
+      type: 'string',
+      required: true
     },
     reg: {
       type: 'string'

index.js

@@ -202,6 +202,12 @@ function buildArray (schema, code, name) {
 function nested (laterCode, name, key, schema) {
   var code = ''
   var funcName
+  if (schema.required) {
+    code += `
+      if (!obj.hasOwnProperty('${key.slice(1)}')) {
+        throw new Error('${key} is required!')
+      }`
+  }
   const type = schema.type
   switch (type) {
     case 'null':

test.js

@@ -254,3 +254,41 @@ test('object with RexExp', (t) => {
   t.equal(obj.reg.source, new RegExp(JSON.parse(output).reg).source)
   t.ok(validate(JSON.parse(output)), 'valid schema')
 })
+
+test('object with required field', (t) => {
+  t.plan(3)
+
+  const schema = {
+    title: 'object with required field',
+    type: 'object',
+    properties: {
+      str: {
+        type: 'string',
+        required: true
+      },
+      num: {
+        type: 'integer'
+      }
+    }
+  }
+  const stringify = build(schema)
+
+  try {
+    stringify({
+      str: 'string'
+    })
+    t.pass()
+  } catch (e) {
+    t.fail()
+  }
+
+  try {
+    stringify({
+      num: 42
+    })
+    t.fail()
+  } catch (e) {
+    t.is(e.message, '.str is required!')
+    t.pass()
+  }
+})