可以参考下这个 移动屏幕适配

利用screen.width并结合viewport标签：

To reliably use JavaScript to retrieve the actual width of the screen a visitor is using , nowadays you have to use the screen.width property in combination with a viewport meta-tag with width=device-width.

文章： Javascript - get device width / screen width on mobile devices

SO上的相关问题：Get the device width in javascript

You can get the device screen width via the screen.width property.
Sometimes it's also useful to use window.innerWidth (not typically found on mobile devices) instead of screen width when dealing with desktop browsers where the window size is often less than the device screen size.

Typically, when dealing with mobile devices AND desktop browsers I use the following:

var width = (window.innerWidth > 0) ? window.innerWidth : screen.width;