feat(CountDown): support SS and S format (#5154)

src/count-down/test/__snapshots__/index.spec.js.snap

@@ -5,3 +5,7 @@ exports[`complete format prop 1`] = `<div class="van-count-down">01-05-59-59-999
 exports[`disable auto-start prop 1`] = `<div class="van-count-down">100</div>`;
 
 exports[`incomplate format prop 1`] = `<div class="van-count-down">29-59-59-999</div>`;
+
+exports[`milliseconds format S 1`] = `<div class="van-count-down">01-5</div>`;
+
+exports[`milliseconds format SS 1`] = `<div class="van-count-down">01-50</div>`;

src/count-down/test/index.spec.js

@@ -141,6 +141,30 @@ test('complete format prop', () => {
   expect(wrapper).toMatchSnapshot();
 });
 
+test('milliseconds format SS', () => {
+  const wrapper = mount(CountDown, {
+    propsData: {
+      time: 1500,
+      autoStart: false,
+      format: 'ss-SS'
+    }
+  });
+
+  expect(wrapper).toMatchSnapshot();
+});
+
+test('milliseconds format S', () => {
+  const wrapper = mount(CountDown, {
+    propsData: {
+      time: 1500,
+      autoStart: false,
+      format: 'ss-S'
+    }
+  });
+
+  expect(wrapper).toMatchSnapshot();
+});
+
 test('incomplate format prop', () => {
   const wrapper = mount(CountDown, {
     propsData: {