detecting mobile browser without user agent sniffing [closed]

Answer 1

You can use the mobile detect JS library to do this. Take note of the warning:

// WARNING: 
//   These JavaScript-based device detection features may ONLY work 
//   for the newest generation of smartphones, such as the iPhone, 
//   Android and Palm WebOS devices.
//   These device detection features may NOT work for older smartphones 
//   which had poor support for JavaScript, including 
//   older BlackBerry, PalmOS, and Windows Mobile devices. 
//   Additionally, because JavaScript support is extremely poor among 
//   'feature phones', these features may not work at all on such devices.
//   For better results, consider using a server-based version of this code, 
//   such as Java, APS.NET, PHP, or Ruby.

Answer 2

there are two options:

1- User Agent sniffing. 2-mobile detect JS library

Answer 3

You just answered your own question - you either want to adopt to user's browser or their device width.

If you want to do something when width is less than WIDTH_CONSTANT you use mediaQueries, or check dimensions with javascript.

Nowadays user agent sniffing is not advised on client side, because rather than sniffing user agent you need to look for the features that you are interested in.

So in your case I am almost confident to say that you should look for device width.

P.S. if you are dealing on server side I think that useragent sniffing would be the only way to find out about device user is using.