[improvement] Field: add clear event (#1944)

packages/field/test/__snapshots__/index.spec.js.snap

@@ -1,5 +1,41 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`clearable 1`] = `
+<div class="van-cell van-field">
+  <!---->
+  <!---->
+  <div class="van-cell__value van-cell__value--alone">
+    <div class="van-field__body">
+      <input type="text" class="van-field__control">
+      <!---->
+      <!---->
+      <!---->
+    </div>
+    <!---->
+  </div>
+  <!---->
+</div>
+`;
+
+exports[`clearable 2`] = `
+<div class="van-cell van-field">
+  <!---->
+  <!---->
+  <div class="van-cell__value van-cell__value--alone">
+    <div class="van-field__body">
+      <input type="text" class="van-field__control">
+      <i class="van-icon van-icon-clear van-field__clear">
+        <!---->
+      </i>
+      <!---->
+      <!---->
+    </div>
+    <!---->
+  </div>
+  <!---->
+</div>
+`;
+
 exports[`render textarea 1`] = `
 <div class="van-cell van-field">
   <!---->

packages/field/test/index.spec.js

@@ -131,3 +131,21 @@ test('maxlength', async() => {
   expect(input.element.value).toEqual('123');
   expect(wrapper.emitted('input')[0][0]).toEqual('123');
 });
+
+test('clearable', () => {
+  const wrapper = mount(Field, {
+    propsData: {
+      value: 'test',
+      clearable: true
+    }
+  });
+
+  expect(wrapper).toMatchSnapshot();
+  const input = wrapper.find('input');
+  input.trigger('focus');
+  expect(wrapper).toMatchSnapshot();
+
+  wrapper.find('.van-field__clear').trigger('touchstart');
+  expect(wrapper.emitted('input')[0][0]).toEqual('');
+  expect(wrapper.emitted('clear')).toBeTruthy();
+});