[improvement] Cell: optimize performance (#1050)

packages/cell/index.ts

@@ -30,24 +30,6 @@ VantComponent({
     }
   },
 
-  computed: {
-    cellClass(): string {
-      const { data } = this;
-      return this.classNames('van-cell', {
-        'van-cell--center': data.center,
-        'van-cell--required': data.required,
-        'van-cell--borderless': !data.border,
-        'van-cell--clickable': data.isLink || data.clickable,
-        [`van-cell--${data.size}`]: data.size
-      });
-    },
-
-    titleStyle(): string {
-      const { titleWidth } = this.data;
-      return titleWidth ? `max-width: ${titleWidth};min-width: ${titleWidth}` : '';
-    }
-  },
-
   methods: {
     onClick(event: Weapp.Event) {
       this.$emit('click', event.detail);

packages/cell/index.wxml

@@ -1,5 +1,7 @@
+<wxs src="../wxs/utils.wxs" module="utils" />
+
 <view
-  class="custom-class {{ cellClass }}"
+  class="custom-class {{ utils.bem('cell', [size, { center, required, borderless: !border, clickable: isLink || clickable }]) }}"
   style="{{ customStyle }}"
   bind:tap="onClick"
 >
@@ -12,7 +14,7 @@
   <slot wx:else name="icon" />
 
   <view
-    style="{{ titleStyle }}"
+    style="{{ titleWidth ? 'max-width:' + titleWidth + ';min-width:' + titleWidth : '' }}"
     class="van-cell__title title-class"
   >
     <block wx:if="{{ title }}">

packages/wxs/bem.wxs

@@ -12,6 +12,10 @@ function join(name, mods) {
 }
 
 function traversing(mods, conf) {
+  if (!conf) {
+    return;
+  }
+
   if (typeof conf === 'string') {
     mods.push(conf);
   } else if (array.isArray(conf)) {