It is common in the US, yes. I've signed a few over the years. I always check the wording of the restrictions to be sure my side projects are clear. And most of the time, the legal counsel for your employer will let you explicitly add on projects as being excluded form the agreement, so you can continue to work on open source projects or prior inventions without having to worry about it.

I definitely recommend that people consult an attorney if they are concerned about the specifics of their own contract. The details of each situation can be quite different.

US employee here - I've signed one (plus a patents & inventions at one firm) at every firm I've worked at since 2000 or so. Thus far any side projects haven't been a problem for them, as I have made sure to target a different industry. But legally, they could have enforced the contract and taken possession of my code.

Even winning a lawsuit costs a lot of money and stress. Unless there is a law that makes courts throw out frivolous lawsuits immediately the employer with lawyers on staff still can make your life very difficult

No doubt. I'm certainly not claiming the current situation is ideal. Just pointing out that it's not always as bad as people think.

Some employers allow a waiver against IP ownership of existing side projects related to the industry.

In France I had a separation in my contract, but I had to disclose and propose to sell my inventions to my employer first.

Wait until you hear about non-compete agreements and such.

I have heard its common in Canada too

Seems to be the case in France as well, i.e, devs don't own their side projects.

Have heard of this happening in Denmark also but never experienced it myself.