perf(empty): use wxs (#3933)

packages/empty/index.ts

@@ -1,7 +1,5 @@
 import { VantComponent } from '../common/component';
 
-const PRESETS = ['error', 'search', 'default', 'network'];
-
 VantComponent({
   props: {
     description: String,
@@ -10,13 +8,4 @@ VantComponent({
       value: 'default',
     },
   },
-  created() {
-    if (PRESETS.indexOf(this.data.image) !== -1) {
-      this.setData({
-        imageUrl: `https://img.yzcdn.cn/vant/empty-image-${this.data.image}.png`,
-      });
-    } else {
-      this.setData({ imageUrl: this.data.image });
-    }
-  },
 });

packages/empty/index.wxml

@@ -1,11 +1,12 @@
 <wxs src="../wxs/utils.wxs" module="utils" />
+<wxs src="./index.wxs" module="computed" />
 
 <view class="custom-class van-empty">
   <view class="van-empty__image">
     <slot name="image"></slot>
   </view>
   <view class="van-empty__image">
-    <image wx:if="{{ imageUrl }}" class="van-empty__image__img" src="{{ imageUrl }}" />
+    <image wx:if="{{ image }}" class="van-empty__image__img" src="{{ computed.imageUrl(image) }}" />
   </view>
 
   <view class="van-empty__description">

packages/empty/index.wxs

@@ -0,0 +1,14 @@
+/* eslint-disable */
+var PRESETS = ['error', 'search', 'default', 'network'];
+
+function imageUrl(image) {
+  if (PRESETS.indexOf(image) !== -1) {
+    return 'https://img.yzcdn.cn/vant/empty-image-' + image + '.png';
+  }
+
+  return image;
+}
+
+module.exports = {
+  imageUrl: imageUrl,
+};