Cascader: fix invalid zero value (#3470)

packages/cascader/src/menu.vue

 <script>
+  import { isDef } from 'element-ui/src/utils/shared';
+
   export default {
     name: 'ElCascaderMenu',
 
@@ -54,7 +56,7 @@
             const level = activeOptions.length;
             activeOptions[level] = options;
             let active = activeValue[level];
-            if (active) {
+            if (isDef(active)) {
               options = options.filter(option => option.value === active)[0];
               if (options && options.children) {
                 loadActiveOptions(options.children, activeOptions);

src/utils/shared.js

+export function isDef(val) {
+  return val !== undefined && val !== null;
+}

test/unit/specs/cascader.spec.js

@@ -96,6 +96,97 @@ describe('Cascader', () => {
       });
     }, 300);
   });
+  // Github issue #3470
+  it('should work with zero', done => {
+    vm = createVue({
+      template: `
+        <el-cascader
+          ref="cascader"
+          placeholder="请选择"
+          :options="options"
+          clearable
+          v-model="selectedOptions"
+        ></el-cascader>
+      `,
+      data() {
+        return {
+          options: [{
+            value: 'zhejiang',
+            label: 'Zhejiang',
+            children: [{
+              value: 0,
+              label: 'Hangzhou',
+              children: [{
+                value: 'xihu',
+                label: 'West Lake'
+              }]
+            }, {
+              value: 'ningbo',
+              label: 'NingBo',
+              children: [{
+                value: 'jiangbei',
+                label: 'Jiang Bei'
+              }]
+            }]
+          }, {
+            value: 'jiangsu',
+            label: 'Jiangsu',
+            children: [{
+              value: 'nanjing',
+              label: 'Nanjing',
+              children: [{
+                value: 'zhonghuamen',
+                label: 'Zhong Hua Men'
+              }]
+            }]
+          }],
+          selectedOptions: []
+        };
+      }
+    }, true);
+    expect(vm.$el).to.be.exist;
+    vm.$el.click();
+    setTimeout(_ => {
+      expect(document.body.querySelector('.el-cascader-menus')).to.be.exist;
+
+      const menu = vm.$refs.cascader.menu;
+      const menuElm = menu.$el;
+      const item1 = menuElm.querySelector('.el-cascader-menu__item');
+
+      item1.click();
+      menu.$nextTick(_ => {
+        expect(menuElm.children.length).to.be.equal(2);
+        expect(item1.classList.contains('is-active')).to.be.true;
+
+        const item2 = menuElm.children[1].querySelector('.el-cascader-menu__item');
+        item2.click();
+
+        menu.$nextTick(_ => {
+          expect(menuElm.children.length).to.be.equal(3);
+          expect(item2.classList.contains('is-active')).to.be.true;
+
+          const item3 = menuElm.children[2].querySelector('.el-cascader-menu__item');
+          item3.click();
+
+          setTimeout(_ => {
+            expect(document.body.querySelector('.el-cascader-menus').style.display).to.be.equal('none');
+            expect(vm.selectedOptions[0]).to.be.equal('zhejiang');
+            expect(vm.selectedOptions[1]).to.be.equal(0);
+            expect(vm.selectedOptions[2]).to.be.equal('xihu');
+
+            triggerEvent(vm.$refs.cascader.$el, 'mouseenter');
+            vm.$nextTick(_ => {
+              vm.$refs.cascader.$el.querySelector('.el-cascader__clearIcon').click();
+              vm.$nextTick(_ => {
+                expect(vm.selectedOptions.length).to.be.equal(0);
+                done();
+              });
+            });
+          }, 500);
+        });
+      });
+    }, 300);
+  });
   it('not allow clearable', done => {
     vm = createVue({
       template: `