Why Javascript, now Iframe or others?

Just wondering why Adsense uses Javascript

[elguapo]

I am not a techie and hence do not know how to write codes and such. But I am just wondering why Adsense uses Javascript? Is it better than Iframe and what are its advantages?

I'm just putting some Amazon codes in my site and noticed that they use Iframes, hence the question

Thanks to anyone and everyone who'll enlighten me

[mrSEman]

Actually G's Javascript code creates an iframe