[bugfix] Popup modal display error

packages/popup/index.vue

@@ -1,6 +1,6 @@
 <template>
   <transition :name="currentTransition">
-    <div v-show="currentValue" class="van-popup" :class="[position ? 'van-popup--' + position : '']">
+    <div v-show="value" class="van-popup" :class="[position ? 'van-popup--' + position : '']">
       <slot></slot>
     </div>
   </transition>
@@ -8,29 +8,23 @@
 
 <script>
 import Popup from '../mixins/popup';
+
 export default {
   name: 'van-popup',
 
   mixins: [Popup],
 
   props: {
+    transition: String,
     overlay: {
       default: true
     },
-
     lockOnScroll: {
       default: false
     },
-
     closeOnClickOverlay: {
       default: true
     },
-
-    transition: {
-      type: String,
-      default: 'popup-slide'
-    },
-
     position: {
       type: String,
       default: ''
@@ -38,31 +32,15 @@ export default {
   },
 
   data() {
+    const transition = this.transition || (this.position === '' ? 'popup-fade' : `popup-slide-${this.position}`);
     return {
       currentValue: false,
-      currentTransition: this.transition
+      currentTransition: transition
     };
   },
 
-  watch: {
-    currentValue(val) {
-      this.$emit('input', val);
-    },
-
-    value(val) {
-      this.currentValue = val;
-    }
-  },
-
-  beforeMount() {
-    if (this.transition !== 'popup-fade') {
-      this.currentTransition = `popup-slide-${this.position}`;
-    }
-  },
-
   mounted() {
     if (this.value) {
-      this.currentValue = true;
       this.open();
     }
   }