Why do you feel you need to prevent it? As a user I'm pretty sure I'd rather just zoom back out if I want to, or use a browser that didn't do this if it really bothered me. But not having the option to zoom is annoying.
As a user I find having to do this incredibly annoying.
Maybe my phone is just a little zealous with the zooming, but it loves to zoom into the top-left corner of the textarea. The first thing I do uses three pinches' worth to zoom back out, and if I ever have to move the cursor and thus touch into the textarea again, it zooms in again.
As a front-end dev, I'm really curious about this. If you're using a native mobile app, do you expect the UI to zoom in on text inputs as well? Is that a common UI behavior?
I've always been a fan of moving mobile web towards the standards and behaviors of native apps which generally did not require zooming to get tasks done.
Yes, it does happen on some text inputs, it tends to depend on relative size (for example, I recall zoom in landscape but not necessarily in portrait, etc.).
Generally I welcome it, because I can click on the teeeny input field and have it come "closer" to me for editing then get out of the way.
