Basically if this is truly something ugly for the US economy and not just a temporary correction, which it doesn't seem to be.. yet.. based on my personal experience circa 2008 as a web developer, here's what I saw from my perspective -
First, older businesses, who have survived other crashes, start tightening their budgets ASAP, pulling back on expensive tech investments. So there's a contraction in big outsourced tech projects with bigger businesses that can start within weeks. If you have big things planned with these guys, close the deal right.now.
Then, many startups who have been too reliant on investor capital for survival get into a pickle when investors stop being as generous dishing out venture and angel rounds. Any company dependent on raising a round of financing in the next 6 months is in a tough place. If you work for any of these guys, polish your resume.
So you start to see layoffs at big consulting firms, then startups start to fail when funds get antsy. This puts a lot of engineering talent on the market, first at job interviews and later for freelance after they've been on the market for a few months. Increased supply means lower salaries and freelance rates. Last time around the big tech cos like Google and Facebook went on a feeding frenzy and drove the supply down, and the mobile thing happened. So salaries bounced back and then went bezerk
I have a feeling if this is another big one, this time around there will be less feeding frenzy and more pruning - the tech giants can use this as an excuse to lay off engineers hired on inflated salaries and not performing. The mobile bubble popped already, and the current bubble is in AI and big data which needs more more specialized brainpower and probably won't pick up a lot of the supply
We also have tons of very junior developers swamping the market with training from coding bootcamps right now. So at the low end of the developer spectrum there's potentially a huge surplus. If things get sour in the market this will be a very tough time for an entry level developer, a pay cut for a mid level developer, and a minor worry for a good developer. For companies with healthy cash reserves, it's a big win though..