网页有三个部分——内容（HTML）、外观（css）、行为（javascript）。
另一个公示：HTML+CSS+JAVASCRIPT=真正的交互性
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javascript has three disadvantages , the problems of concurrence among different web explorers, the structure of DOM is complicated, the development and debugging of javascript is not convenient.
javascript framework has some advantages ,such as the reading of DOM, the operation of DOM, partical functions, handelations of envent, CSS control, data communications (namely, AJAX technicle)
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jquery 适合小型应用开发，
extjs适合大型商业应用，更模块化。
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各类javascript引擎（解释器）对比
