add NavBar component

packages/nav-bar/index.vue

@@ -0,0 +1,38 @@
+<template>
+  <div :class="['van-nav-bar van-hairline--top-bottom', { 'van-nav-bar--fixed': fixed }]">
+    <div class="van-nav-bar__left" @click="$emit('clickLeft')">
+      <slot name="left">
+        <van-icon v-if="leftArrow" class="van-nav-bar__arrow" name="arrow" />
+        <span v-if="leftText" v-text="leftText" class="van-nav-bar__text" />
+      </slot>
+    </div>
+    <div class="van-nav-bar__title">
+      <slot name="title">{{ title }}</slot>
+    </div>
+    <div class="van-nav-bar__right" @click="$emit('clickRight')">
+      <slot name="right">
+        <span v-if="rightText" v-text="rightText" class="van-nav-bar__text" />
+      </slot>
+    </div>
+  </div>
+</template>
+
+<script>
+import Icon from '../icon';
+
+export default {
+  name: 'van-nav-bar',
+
+  components: {
+    [Icon.name]: Icon
+  },
+
+  props: {
+    title: String,
+    leftText: String,
+    rightText: String,
+    leftArrow: Boolean,
+    fixed: Boolean
+  }
+};
+</script>