jquery简介
jquery是js 的库， 所谓库，肯定封装了一些方法，更简洁方便
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简介：
jQuery is a fast, small, and feature-rich JavaScript library.
JQuery是快速，小巧，功能丰富的js库
It makes things like HTML document traversal and manipulation, event handling, animation, and Ajax much simpler with an easy-to-use API that works across a multitude of browsers.
它能通过一个简单的API让html的document在各种浏览器中遍历以及操作, 事件处理，动画还有ajax更加简单
With a combination of versatility and extensibility, jQuery has changed the way that millions of people write JavaScript.
通过整合多样性与扩展性， jQuery改变了百万人写js的方式