当到屏幕的某个位置，执行命令

$(function()
{
$(window).scroll(function(){


if($(window).scrollTop() >= $("#sec2").offset().top-300){

$("#sec2 .squre6 h2").show().css("-webkit-animation","fourtext 0.5s 1 ease-in");
$("#sec2 .squre6 p").show().css("-webkit-animation","fourtext 0.5s 1 ease-in");

$("#sec2 .squre6 h2").show().css("-moz-animation","fourtext 0.5s 1 ease-in");
$("#sec2 .squre6 p").show().css("-moz-animation","fourtext 0.5s 1 ease-in");

$("#sec2 .squre6 h2").show().css("-ms-animation","fourtext 0.5s 1 ease-in");
$("#sec2 .squre6 p").show().css("-ms-animation","fourtext 0.5s 1 ease-in");

$("#sec2 .squre6 h2").show().css("-o-animation","fourtext 0.5s 1 ease-in");
$("#sec2 .squre6 p").show().css("-o-animation","fourtext 0.5s 1 ease-in");

};

});

})

当到屏幕的某个位置，执行命令

原文：http://www.cnblogs.com/zmeieasyjob/p/4220677.html