Using jquery to determine screen width

JQuery uses $(window).width(). It's a function, not a property.

iPhone6 screen is 1334x750 pixels. If you only use the width to detect mobile user, see this instead.

The iPhone 6 display has a resolution of 1334x750. When emulating iPhone6 in chrome dev tools the width is reported as 980 (I don't know if this is accurate).

You might be interested in this: http://detectmobilebrowsers.com/

Also, as others have noted, replace $(window).width with $(window).width()

Well, ignoring what ekuusela said about screen resolution, you seem to have forgotten your parentheses after width, which is a method, not a field. To fix this, just add () after it:

if ($(window).width() < 700)

See the documentation for width() for more info.