diff --git a/components/dropdown/dropdown-button.tsx b/components/dropdown/dropdown-button.tsx
index 3a90d26b10..225aa1ae6a 100644
--- a/components/dropdown/dropdown-button.tsx
+++ b/components/dropdown/dropdown-button.tsx
@@ -70,7 +70,7 @@ const DropdownButton: DropdownButtonInterface = props => {
   } = props;
 
   const prefixCls = getPrefixCls('dropdown-button', customizePrefixCls);
-  const dropdownProps = {
+  const dropdownProps: DropdownProps = {
     align,
     overlay,
     disabled,
@@ -82,7 +82,7 @@ const DropdownButton: DropdownButtonInterface = props => {
     overlayClassName,
     overlayStyle,
     destroyPopupOnHide,
-  } as DropdownProps;
+  };
 
   if ('open' in props) {
     dropdownProps.open = open;
@@ -113,7 +113,7 @@ const DropdownButton: DropdownButtonInterface = props => {
 
   const rightButton = <Button type={type} danger={danger} icon={icon} />;
 
-  const [leftButtonToRender, rightButtonToRender] = buttonsRender!([leftButton, rightButton]);
+  const [leftButtonToRender, rightButtonToRender] = buttonsRender([leftButton, rightButton]);
 
   return (
     <ButtonGroup {...restProps} className={classNames(prefixCls, className)}>
diff --git a/components/dropdown/dropdown.tsx b/components/dropdown/dropdown.tsx
index bf3ef5bc1f..f14096e14a 100644
--- a/components/dropdown/dropdown.tsx
+++ b/components/dropdown/dropdown.tsx
@@ -109,7 +109,7 @@ const Dropdown: DropdownInterface = props => {
     if (transitionName !== undefined) {
       return transitionName;
     }
-    if (placement.indexOf('top') >= 0) {
+    if (placement.includes('top')) {
       return `${rootPrefixCls}-slide-down`;
     }
     return `${rootPrefixCls}-slide-up`;
@@ -118,7 +118,7 @@ const Dropdown: DropdownInterface = props => {
   const getPlacement = () => {
     const { placement } = props;
     if (!placement) {
-      return direction === 'rtl' ? ('bottomRight' as Placement) : ('bottomLeft' as Placement);
+      return direction === 'rtl' ? 'bottomRight' : 'bottomLeft';
     }
 
     if (placement.includes('Center')) {
@@ -146,6 +146,8 @@ const Dropdown: DropdownInterface = props => {
     open,
     onVisibleChange,
     onOpenChange,
+    mouseEnterDelay = 0.15,
+    mouseLeaveDelay = 0.1,
   } = props;
 
   const prefixCls = getPrefixCls('dropdown', customizePrefixCls);
@@ -163,8 +165,8 @@ const Dropdown: DropdownInterface = props => {
   });
 
   const triggerActions = disabled ? [] : trigger;
-  let alignPoint;
-  if (triggerActions && triggerActions.indexOf('contextMenu') !== -1) {
+  let alignPoint: boolean;
+  if (triggerActions && triggerActions.includes('contextMenu')) {
     alignPoint = true;
   }
 
@@ -198,9 +200,9 @@ const Dropdown: DropdownInterface = props => {
     // So we need render the element to check and pass back to rc-dropdown.
     const { overlay } = props;
 
-    let overlayNode;
+    let overlayNode: React.ReactNode;
     if (typeof overlay === 'function') {
-      overlayNode = (overlay as OverlayFunc)();
+      overlayNode = overlay();
     } else {
       overlayNode = overlay;
     }
@@ -236,8 +238,10 @@ const Dropdown: DropdownInterface = props => {
   // ============================ Render ============================
   return (
     <RcDropdown
-      alignPoint={alignPoint}
+      alignPoint={alignPoint!}
       {...props}
+      mouseEnterDelay={mouseEnterDelay}
+      mouseLeaveDelay={mouseLeaveDelay}
       visible={mergedOpen}
       builtinPlacements={builtinPlacements}
       arrow={!!arrow}
@@ -257,9 +261,4 @@ const Dropdown: DropdownInterface = props => {
 
 Dropdown.Button = DropdownButton;
 
-Dropdown.defaultProps = {
-  mouseEnterDelay: 0.15,
-  mouseLeaveDelay: 0.1,
-};
-
 export default Dropdown;