jQuery is used due to following advantages.
1.Easy to use and learn.
3.Cross-browser support (IE 6.0+, FF 1.5+, Safari 2.0+, Opera 9.0+)
4.Easy to use for DOM manipulation and traversal.
5.Large pool of built in methods.
7.Methods for changing or applying CSS, creating animations.
8.Event detection and handling.
9.Tons of plug-ins for all kind of needs.