Does the iframe have any effect on page load time? Why not?

Like the headline says: What开发者_开发问答 effect does iframe have on page load time? Thanks.

iFrames are somewhat costly, even when left blank when compared with other HTML elements. The biggest drawback is that they block the window onload event until complete, which can make the users perceive that the page they requested is slow.

The do have their uses though in allowing you to compartmentalize external web pages or sandboxing another DOM structure outside of the main page.

Here is a good article on them