feat(layer): 新增 btnAsync 选项 (#2002)

* feat(layer): 新增 btnAsync 选项

* docs(layer): 添加 btnAsync 文档

* docs(layer): 添加 btnAsync 示例

* refactor: 删除按钮回调中的 loading 参数

* feat(layer): beforeEnd 回调新增第三个参数

* docs(layer): 更新文档

* docs: 优化 btnAsync 选项文档细节

* chore: 优化细节及增加注释

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Co-authored-by: 贤心 <3277200+sentsim@users.noreply.github.com>

docs/layer/examples/btnasync.md

@@ -0,0 +1,90 @@
+<button type="button" class="layui-btn layui-btn-primary" lay-on="bs_alert">alert</button>
+<button type="button" class="layui-btn layui-btn-primary" lay-on="bs_confirm">confirm</button>
+<button type="button" class="layui-btn layui-btn-primary" lay-on="bs_msg">msg</button>
+<button type="button" class="layui-btn layui-btn-primary" lay-on="bs_open">open</button>
+<button type="button" class="layui-btn layui-btn-primary" lay-on="bs_prompt">prompt(不支持)</button>
+
+<!-- import layui -->
+<script>
+layui.use(function () {
+  var $ = layui.$
+  var util = layui.util;
+  var sleep = function (time) {
+    return $.Deferred(function (defer) {
+      setTimeout(function () {
+        defer.resolve();
+      }, time)
+    })
+  }
+  var enableBtnAsync = true;
+
+  util.on({
+    bs_alert: function () {
+      layer.alert('对话框内容', {
+        btnAsync: enableBtnAsync,
+      }, function (index, layero, that) {
+        var defer = $.Deferred();
+        that.loading(true);
+        sleep(1000).then(defer.resolve);
+        return defer.promise();
+      });
+    },
+    bs_confirm: function () {
+      layer.confirm('一个询问框的示例？', {
+        btnAsync: enableBtnAsync,
+        btn: ['确定', '关闭'] //按钮
+      }, function (index, layero, that) {
+        var defer = $.Deferred();
+        that.loading(true);
+        sleep(1000).then(defer.resolve);
+        return defer.promise();
+      });
+    },
+    bs_msg: function () {
+      layer.msg('第二个回调', {
+        btnAsync: enableBtnAsync,
+        time: 20000, // 20s 后自动关闭
+        btn: ['明白了', '知道了'],
+        btn1: function (index, layero, that) {
+          var defer = $.Deferred();
+          that.loading(true);
+          sleep(1000).then(defer.resolve);
+          return defer.promise();
+        }
+      });
+    },
+    bs_open: function () {
+      layer.open({
+        btnAsync: enableBtnAsync,
+        type: 1,
+        area: ['500px', '300px'],
+        btn: ['确定', '关闭'],
+        btn1: function (index, layero, that) {
+          var defer = $.Deferred();
+          that.loading(true);
+          sleep(1000).then(defer.resolve);
+          return defer.promise();
+        },
+        btn2: function (index, layero, that) {
+          var defer = $.Deferred();
+          that.loading(true);
+          sleep(1000).then(defer.resolve);
+          return defer.promise();
+        }
+      })
+    },
+    // 不支持 btnAsync
+    bs_prompt: function () {
+      layer.prompt({
+        formType: 2,
+        value: '初始值',
+        title: '请输入值',
+        area: ['500px', '300px'] // 自定义文本域宽高
+      }, function (value, index, elem) {
+        alert(value);
+        layer.close(index);
+      });
+    }
+  })
+}); 
+</script>