【導(dǎo)讀】了推動類型系統(tǒng)分析，靜態(tài)分析和編譯技術(shù)研究等領(lǐng)域發(fā)展的動力之一。員是如何利用語言的這些特性。在本文中，我們將研究一些廣泛使用JavaScript. 用工業(yè)標(biāo)準(zhǔn)中的數(shù)據(jù)進(jìn)行比較。至是結(jié)構(gòu)化編程。與之對應(yīng)的是，JavaScript十分強(qiáng)調(diào)編程語言的靈活性。JavaScript的成功是不可否認(rèn)的。據(jù)相關(guān)數(shù)據(jù)顯示，當(dāng)前最流行的100個網(wǎng)站中。以及開發(fā)環(huán)境等的通用計算平臺。它一直被譽(yù)為互聯(lián)網(wǎng)界的“匯編語言”，和Java. 以及Scheme語言類似，JavaScript需要代碼生成工具的解釋。工具，以幫助開發(fā)者盡早的發(fā)現(xiàn)程序中的漏洞。JavaScript實(shí)現(xiàn)很大的進(jìn)步，目前最先進(jìn)的即時編譯技術(shù)得到了應(yīng)用。驗(yàn)證現(xiàn)有的JavaScript程序。的擴(kuò)展的類型檢查。對于JavaScript，Anderson等人提。常見的關(guān)于JavaScript的動態(tài)行為的假設(shè)。那么具體到JavaScript的情形，就是假設(shè)作。JavaScript里的類型系統(tǒng)已經(jīng)聲明的。JavaScript允許不同元數(shù)的調(diào)用。一些出色的JavaScript程序的完善和優(yōu)化，如。本文的目的是提供支持或否定以上假設(shè)的證據(jù)。

　　

【正文】 e consistent with the newresults presented here. Holkner and Harland have conducted a study of the use of dynamic features (addition and deletion of fields and methods) in the Python programming language. Their study focused on a smaller set of programs and concluded that there is a clear phase distinction. In their corpus dynamic features occur mostly in the initialization phase of programs and less so during the main putation. Our results suggest that JavaScript is more dynamic than Python in practice. There are many studies of the runtime use of selected features of objectoriented languages. For example, Garret et al. reported on the dynamism of message sends in Self , Calder et al. characterized the difference of between C and C++ programs in , and Temporo et al. studied the usage of inheritance in Java in . These previous papers study in great detail one particular aspect of each language. In this particular work, we strive for an overview of JavaScript, and leave detailed analysis for future work. Finally, we were inspired by the work of Dufour et al. and their rigorous framework for discussing runtime metrics for Java. 3. Tracing and Analysis Infrastructure The tracing infrastructure developed for this paper is based on an instrumented version of the WebKit web browser engine integrated into Apple’s Safari browser. While there are standalone interpreters available, they would not be able to deal with the mixture of DOM and AJAX that is monplace in most JavaScriptenabled sites. For flexibility, analysis is performed offline. Our instrumented browser records a trace containing most operations performed by the interpreter (reads, writes,deletes, calls,defines,etc.)as well as events for garbage collection and source file loads. Invocations to eval trigger an event similar to the one for source file loads, and the 中原工學(xué)院信息商務(wù)學(xué)院畢業(yè)設(shè)計（論文）譯文專用紙 第 12頁 evaluated string is saved and traced like any other part of the program’s execution. Complete traces are pressed and stored to disk. While it does have some performance overhead, our instrumentation does not cause a noticeable slowdown in interactive applications, and none of our users plained about performance. Traces are analyzed offline and the results are stored in a database which is then mined for data. The offline trace analysis ponent is essentially an abstract interpreter for the event stream. It is able to replay any trace creating an abstract representation of the heap state of the corresponding JavaScript program. The trace analyzer maintains rich and customizable historical information about the program’s behavior, such as access histories of each object, call sites and allocation sites, and so on. Finally, several static analyses (eval classification, code size metrics) are performed on the recovered source files using the parsing framework from the Rhino JavaScript piler. 4. Conclusion This paper has provided the first largescale study of the runtime behavior of JavaScript programs. We have identified a set of representative realworld programs ranging in size from hundreds of kilobytes to megabytes, using an instrumented interpreter we have recorded multiple traces per site, and then with an offline analysis tool we have extracted behavioral information from the traces. We use this information to evaluate a list of nine monly made assumptions about JavaScript programs.