在上篇文章给大家介绍了javascript jquery ajax的小结，今天接着给大家介绍javascript jquery与ajax的关系，感兴趣的朋友一起学习吧
简单总结：
1、JS是一门前端语言。
2、Ajax是一门技术，它提供了异步更新的机制，使用客户端与服务器间交换数据而非整个页面文档，实现页面的局部更新。
3、jQuery是一个框架，它对JS进行了封装，使其更方便使用。jQuery使得JS与Ajax的使用更方便
详细情况：
Actually only one of them is a programming language.
Javascript is a programming language which is used mainly in webpages for making websites interactive. When a webpage is parsed by the browser, it creates an in-memory representation of the page. It is a tree structure, which contains all elements on the page. So there is a root element, which contains the head and the body elements, which contain other elements, which contain other elements. So it looks like a tree basically. Now with javascript you can manipulate elements in the page using this tree. You can pick elements by their id (getElementsById), or their tag name (getElementsByTagName), or by simply going through the tree (parentNode, firstChild, lastChild, nextSibling, previousSibling, etc.). Once you have element(s) to work with you can modify them by changing their look, content or position on the page. This interface is also known as the DOM(Document Object Model). So you can do everything with Javascript that another programming language can do, and by using it embedded into wepages you also get an in-memory Object of the current webpage by which you can make changes to the page interactively.
AJAX is a technique of communication between the browser and the server within a page. Chat is a good example. You write a message, send a message and recive other messages without leaving the page. You can manage this interaction with Javascript on the client side, using an XMLHTTP Object provided by the browser.
jQuery is a library which aims to simplify client side web development in general (the two other above). It creates a layer of abstracion so you can reuse common languages like CSS and HTML in Javascript. It also includes functions which can be used to communicate with servers very easily (AJAX). It is written in Javascript, and will not do everything for you, only makes common tasks easier. It also hides some of the misconceptions and bugs of browsers.
To sum up:
Javascript is a programming language (objects, array, numbers, strings, calculations)
AJAX and jQuery uses Javascript
jQuery is for simplifing common tasks with AJAX and page manipulation (style, animation, etc.)
Finally, an example just to see some syntax:
// page manipulation in javascript
var el = document.getElementById("box");
el.style.backgroundColor = "#000";
var new_el = document.createElement("div");
el.innerHTML = "<p>some content</p>";
el.appendChild(new_el);
// and how you would do it in jQuery
$("#box")
.css({ "background-color": "#000" })
.append("<div><p>some content</p></div>");
1.javascript是一种在客户端执行的脚本语言。ajax是基于javascript的一种技术，它主要用途是提供异步刷新（只刷新页面的一部分，而不是整个页面都刷新）。一个是语言,一个是技术,两者有本质区别.
2.javascript是一种在浏览器端执行的脚本语言，Ajax是一种创建交互式网页应用的开发技术 ，它是利用了一系列相关的技术其中就包括javascript。
3.
JavaScript可以做什么？
用JavaScript可以做很多事情，使网页更具交互性，给站点的用户提供更好,更令人兴奋的体验。JavaScript使你可以创建活跃的用户界面，当用户在页面间导航时向他们反馈。
使用JavaScript来确保用户以表单形式输入有效的信息，这可以节省你的业务时间和开支。
使用JavaScript，根据用户的操作可以创建定制的HTML页面。
JavaScript还可以处理表单，设置cookie，即时构建HTML页面以及创建基于Web的应用程序。
JavaScript不能做什么？
JavaScript是一种客户端语言。（实际上，也存有服务器端实现的JavaScript版本）。也就是说，设计它的目的是在用户的机器上执行任务，而不是在服务器上。因此，JavaScript有一些固有的限制，这些限制主要出于如下安全原因：
1.JavaScript不允许读写客户机器上的文件。这是有好处的，因为你肯定不希望网页能够读取自己硬盘上的文件，或者能够将病毒写入硬盘，或者能够操作你的计算机上的文件。唯一例外是，JavaScript可以写到浏览器的cookie文件，但是也有一些限制。
2.JavaScript不允许写服务器机器上的文件。尽管写服务器上的文件在许多方面是很方便的（比如存储页面点击数或用户填写表单的数据），但是JavaScript不允许这么做。相反，需要用服务器上的一个程序处理和存储这些数据。这个程序可以是Perl或者PHP等语言编写的CGI运行在服务器上的程序或者Java程序
3.JavaScript不能关闭不是它自己打开的窗口。这是为了避免一个站点关闭其他任何站点的窗口，从而独占浏览器。