Dynamic form and alternatives to captcha to avoid form spam

I was wondering, if i'm not wrong the spam robots parse the html source at loading time to detect the presence of 开发者_运维百科a form, am I right?

Would the be of any protection to generate the form dynamically with javascript? (of course you would need js enabled, i wonder who doesn't today)

Another idea i had. I never liked captcha, they stop user flow and if you are wrong you will have to reload the page. I was thinking about an iphone like sliding widget. would it be impossible for robots to get through it, isn't it?

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Consider the accessibility of any alternative you use to block your spam. Can someone with a visual, mobility or cognitive impairment operate the sliding widget to submit your form? If they cannot, and there is no alternative, such as an audio option, then you are limiting who can submit your form to those without accessibility issues.

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I use javascript to dynamically add a field to all submits, the server ignores any incoming form submissions that don't have it.

It reduces the spam, but isn't a magic bullet. I still get seo spam now and then, on my sight that gets hardly any traffic. They either have 3rd world slaves manually doing form submission, or their form scraping is smart enough to figure out javascript tricks.