Cascader: Add before-filter hook

examples/docs/en-US/cascader.md

@@ -1656,6 +1656,7 @@ Search and select options with a keyword.
 | value     | specify which key of option object is used as the option's value | string | — | — |
 | children  | specify which key of option object is used as the option's child options | string | — | — |
 | disabled  | specify which key of option object indicates if the option is disabled | string | — | — |
+| before-filter | hook function before filtering with the value to be filtered as its parameter. If `false` or a `Promise` is returned, filtering will be aborted | function(value) | — | — |
 
 ### Events
 | Event Name | Description | Parameters |

examples/docs/zh-CN/cascader.md

@@ -1687,6 +1687,7 @@
 | label    | 指定选项标签为选项对象的某个属性值 | string | — | — |
 | children | 指定选项的子选项为选项对象的某个属性值 | string | — | — |
 | disabled | 指定选项的禁用为选项对象的某个属性值 | string | — | — |
+| before-filter | 可选参数, 筛选之前的钩子，参数为输入的值，若返回 false 或者 Promise 则停止筛选。 | function(value) | — | — |
 
 ### Events
 | 事件名称      | 说明    | 回调参数      |

packages/cascader/src/main.vue

@@ -139,6 +139,10 @@ export default {
     debounce: {
       type: Number,
       default: 300
+    },
+    beforeFilter: {
+      type: Function,
+      default: null
     }
   },
 
@@ -328,8 +332,27 @@ export default {
 
   created() {
     this.debouncedInputChange = debounce(this.debounce, value => {
+      const before = this.beforeFilter(value);
+
+      if (before && before.then) {
+        this.menu.options = [{
+          __IS__FLAT__OPTIONS: true,
+          label: this.t('el.cascader.loading'),
+          value: '',
+          disabled: true
+        }];
+        before
+          .then(() => {
+            this.$nextTick(() => {
               this.handleInputChange(value);
             });
+          });
+      } else if (before !== false) {
+        this.$nextTick(() => {
+          this.handleInputChange(value);
+        });
+      }
+    });
   },
 
   mounted() {

src/locale/lang/en.js

@@ -62,6 +62,7 @@ export default {
     },
     cascader: {
       noMatch: 'No matching data',
+      loading: 'Loading',
       placeholder: 'Select'
     },
     pagination: {

src/locale/lang/zh-CN.js

@@ -62,6 +62,7 @@ export default {
     },
     cascader: {
       noMatch: '无匹配数据',
+      loading: '加载中',
       placeholder: '请选择'
     },
     pagination: {