When you load content from a URL, the default value is undefined until the load operation has started.

从URL加载内容时，直到开始加载操作，才会定义默认值。

youdao

When you load content from a URL, the default value is undefined until the load operation has started.

从URL加载内容时，直到开始加载操作，才会定义默认值。

youdao