fix(render): improve JsonpJSON content type handling and simplify Context.JSONP

context.go

@@ -1135,13 +1135,10 @@ func (c *Context) SecureJSON(code int, obj any) {
 // JSONP serializes the given struct as JSON into the response body.
 // It adds padding to response body to request data from a server residing in a different domain than the client.
 // It also sets the Content-Type as "application/javascript".
+//
+// When the callback parameter is empty, it behaves equivalently to Context.JSON.
 func (c *Context) JSONP(code int, obj any) {
-	callback := c.DefaultQuery("callback", "")
-	if callback == "" {
-		c.Render(code, render.JSON{Data: obj})
-		return
-	}
-	c.Render(code, render.JsonpJSON{Callback: callback, Data: obj})
+	c.Render(code, render.JsonpJSON{Callback: c.Query("callback"), Data: obj})
 }
 
 // JSON serializes the given struct as JSON into the response body.

render/json.go

@@ -115,17 +115,19 @@ func (r SecureJSON) WriteContentType(w http.ResponseWriter) {
 
 // Render (JsonpJSON) marshals the given interface object and writes it and its callback with custom ContentType.
 func (r JsonpJSON) Render(w http.ResponseWriter) (err error) {
-	r.WriteContentType(w)
 	ret, err := json.API.Marshal(r.Data)
 	if err != nil {
 		return err
 	}
 
 	if r.Callback == "" {
+		writeContentType(w, jsonContentType)
 		_, err = w.Write(ret)
 		return err
 	}
 
+	r.WriteContentType(w)
+
 	callback := template.JSEscapeString(r.Callback)
 	if _, err = w.Write(bytesconv.StringToBytes(callback)); err != nil {
 		return err

render/render_test.go

@@ -183,19 +183,28 @@ func TestRenderJsonpJSONError(t *testing.T) {
 	assert.Equal(t, `write "`+`);`+`" error`, err.Error())
 }
 
-func TestRenderJsonpJSONError2(t *testing.T) {
+func TestRenderJsonpJSONWithEmptyCallback(t *testing.T) {
 	w := httptest.NewRecorder()
 	data := map[string]any{
 		"foo": "bar",
+		"num": 42,
+		"nested": map[string]any{
+			"key": "value",
+		},
 	}
-	(JsonpJSON{"", data}).WriteContentType(w)
-	assert.Equal(t, "application/javascript; charset=utf-8", w.Header().Get("Content-Type"))
 
-	e := (JsonpJSON{"", data}).Render(w)
-	require.NoError(t, e)
+	err := (JsonpJSON{Callback: "", Data: data}).Render(w)
 
-	assert.JSONEq(t, "{\"foo\":\"bar\"}", w.Body.String())
-	assert.Equal(t, "application/javascript; charset=utf-8", w.Header().Get("Content-Type"))
+	require.NoError(t, err)
+
+	// Verify Content-Type is set to jsonContentType when callback is empty
+	assert.Equal(t, "application/json; charset=utf-8", w.Header().Get("Content-Type"))
+
+	renderData, err := json.API.Marshal(data)
+	require.NoError(t, err)
+
+	// Verify body contains correct JSON data
+	assert.JSONEq(t, string(renderData), w.Body.String())
 }
 
 func TestRenderJsonpJSONFail(t *testing.T) {