先看看官方帮助上的英文：
If you want to embed lightweight mapping functionality into a Web application, or if you're just getting started with ArcGIS Server development, consider using the ArcGIS JavaScript API. It's free to use and deploy applications built with this API. All you need is an ArcGIS Server available whose maps and tools you can use in your application. To get started, see the ArcGIS JavaScript API home page.
The ArcGIS JavaScript API is powered by a back-end REST API that is able to retrieve information statelessly from the server. When you run the application, the code runs in the browser instead of having to run on the server. This provides a quick and clean client experience. The ArcGIS JavaScript API is built on top of the Dojo JavaScript toolkit, so you don't have to worry about accommodating browser idiosyncrasies in your code; the framework handles it for you.
You can use the ArcGIS JavaScript API even if you have little or no coding experience. Copy and paste the example code into your HTML pages to add mapping functionality.
When writing applications with the ArcGIS JavaScript API, you'll need to provide the URLs to maps and other resources on your server. You can use the ArcGIS Services Directory to find out these Web addresses. For examples, see the Services Directory Help page at http://<server name>/<instance name>/SDK/REST/servicesdirectory.html.
ArcGIS Server also includes extensions for well-known online mapping APIs for JavaScript:
· ArcGIS JavaScript Extension for the Google Maps API
This extension for the Google Maps API allows you to integrate your maps with the Google Maps base layers. You can perform query and geoprocessing tasks on your services and work with the results as features. You can also publish your content as a Google Mapplet.
To get started, see the ArcGIS JavaScript Extension for the Google Maps API home page.
· ArcGIS JavaScript Extension for Virtual Earth
This extension for Microsoft Virtual Earth allows you to display your maps over the Virtual Earth base maps in 2D or 3D. You can perform query and geoprocessing tasks on your services and work with the results as VEShapes. You can also perform geocoding operations and view the results on the base map.
To get started, see the ArcGIS JavaScript Extension for Virtual Earth home page.
These two extensions can be useful if you're already familiar with the Virtual Earth or Google Maps APIs or you want to use the basemaps provided by these services. If you decide to use the ArcGIS JavaScript API, you can use the basemaps provided by ArcGIS Online.
Google翻译结果：
如果你想嵌入轻量级映射功能集成到一个Web应用程序，或者如果您刚开始使用ArcGIS的服务器的发展，考虑使用ArcGIS的JavaScript的空气污染指数。它是免费的使用和部署应用程序建立与此API 。您只需要一个ArcGIS的服务器提供的地图和工具，您可以使用您在申请中。要开始，请参阅教程的JavaScript API的主页。 该教程的JavaScript API是由后端的REST的API ，能够检索信息statelessly从服务器。当您运行该应用程序，代码运行在浏览器中而不是在服务器上运行。这提供了一种快速和清洁的客户体验。该教程的JavaScript API是建立在道场的JavaScript工具包，这样您就不必担心浏览器的特性可容纳在您的代码;它的框架内为您处理。 您可以使用JavaScript的扩展模块的API ，即使你很少或没有编码经验。复制并粘贴示例代码到您的HTML网页添加映射功能。 写作时的应用与扩展模块的JavaScript API ，您将需要提供的网址，以地图和其他资源在您的服务器上。您可以使用ArcGIS的服务指南，了解这些Web地址。举例来说，看到服务指南帮助页面位于http:// <服务器名称> / <instance名称/ SDK中/休息/ servicesdirectory.html 。 ArcGIS的服务器还包括扩展众所周知的在线地图的API对JavaScript ： • ArcGIS的JavaScript的延长谷歌地图API 这一扩展的谷歌地图API允许您将您的地图与谷歌地图的基础层。您可以执行的任务查询和geoprocessing在您的服务和工作的成果为特征。您也可以发布您的内容，作为谷歌的Mapplet 。 要开始，请参阅教程JavaScript的延长谷歌地图API主页。 • ArcGIS的JavaScript的扩展虚拟地球 这一延长对微软虚拟地球让您展示您的地图的虚拟地球底图在二维或三维。您可以执行的任务查询和geoprocessing在您的服务和工作的结果作为VEShapes 。您还可以执行地理编码操作和查看结果的基础上，地图。 要开始，请参阅教程JavaScript的扩展虚拟地球主页。 这两个扩展可以是有用的，如果您已经熟悉虚拟地球或谷歌地图API或您要使用basemaps提供这些服务。如果您决定使用该教程的JavaScript API ，您可以使用所提供的ArcGIS的basemaps在线。
The ArcGIS API for JavaScript™ (JavaScript API) is a browser based API for developing high performance, easy to use mapping applications. The API allows you to easily embed maps in your Web pages.
The JavaScript API is hosted by ESRI on ArcGIS Online and is available for free use.
我们可以知道，这个API是为开发高级的地图浏览而设计的，其功能强大，使用也很简单。其使用的资源包是在ArcGIS Online提供的！只需引用即可！！