按id定位元素 [英] Locating an element by id

问题描述

以下位置技术有什么区别？

1. 元素（by.id（id ））;


2. 元素（by.css（＃id））;


3. 元素（by.xpath（// * [@ id ='id']））;


4. browser.executeScript（return document.querySelector（'＃id'）;）;


5. browser.executeScript（return document.getElementById（'id'）;）;

解决方案

从性能角度来看，这将是以最快的方式定位元素。

你的问题很难回答，肯定会给一个单一的结论性答案。事实上，我试图将这个问题标记为太广泛，这得到了其他答案和评论的支持。

例如， c $ c> element（by.id（id））; 。通过Selenium源，大多数驱动程序只需接受您提供的任何ID，并将其传递到有线协议：

  public WebElement findElementById（String using）{
 if（getW3CStandardComplianceLevel（）== 0）{
 return findElement（id，using）; 
} else {
 return findElementByCssSelector（＃+ cssEscape（using））; 
} 
} 
  

如你所知，协议在一个单独的二进制。

对于不支持wire协议的其他浏览器，例如HtmlUnit，你只需要具有类似：

  public List< WebElement> findElementsById（String id）{
 return findElementsByXPath（// * [@ id ='+ id +']）; 
} 
  

，然后解析可用的DOM。

对于你的性能问题，任何人给你的任何东西都将是1）只是一个感觉，或2）纯BS！

要获得真实的回答（由实际数据支持），您可以从其他回答和评论中看到。

• 由不同浏览器供应商实施的连线协议，以及不同版本的各种优化。


• 由不同浏览器供应商实施的DOM引擎，以及不同版本的各种优化。


• 由不同浏览器供应商实施的JavaScript引擎，以及不同版本的各种优化。

此外，无论您的网络应用/网页的结果如何，都不适用于其他网络应用/网页，由于用于构建该网站的框架的差异。

底线是：如果你关心性能测试，那么Selenium是错误的答案。 Selenium是一个功能测试库，优化为您提供最好的最终用户表示。

如果你的目标是让你的测试运行得更快，你的时间将更好地考虑你的测试结构：

• 您打开/关闭浏览器的频率。这通常是测试中最耗时的活动。


• 您多久刷新一次元素缓存，您需要多久？考虑将您的元素移动到页面工厂模型，它会延迟加载所有元素。


• 当然最大的加速因子：并行运行测试多个机器。

但是我认为这是从你的初始问题的主题（有些可能建议ranty）。 >

What is the difference between the following location techniques?

1. element(by.id("id"));
2. element(by.css("#id"));
3. element(by.xpath("//*[@id='id']"));
4. browser.executeScript("return document.querySelector('#id');");
5. browser.executeScript("return document.getElementById('id');");

And, from the performance perspective, which would be the fastest way to locate an element by id?

解决方案

Your question is very difficult to answer, certainly to give a single conclusive answer. In fact, I am tempted to flag this question as "too broad", which is supported by the other answers and comments.

Take, for example, just your element(by.id("id"));. Looking through the Selenium source, most drivers just take whatever id you give, and pass it off to the wire protocol:

public WebElement findElementById(String using) {
  if (getW3CStandardComplianceLevel() == 0) {
    return findElement("id", using);
  } else {
    return findElementByCssSelector("#" + cssEscape(using));
  }
}

As you know, each browser vendor implements their own wire protocol in a separate binary. Feel free to go further into the code, to dig a deeper hole for your self.

For other browsers that do not support the wire protocol, for example HtmlUnit, you just have something like:

public List<WebElement> findElementsById(String id) {
  return findElementsByXPath("//*[@id='" + id + "']");
}

and then they parse the available DOM.

As for your performance question, anything that anyone gives you will be 1) just a feeling, or 2) pure BS! Which you can already see from the other answers and comments you are getting.

To get a real answer (supported by actual data), there are just too many variables to consider:

• Wire protocol as implemented by different browser vendors, plus various optimizations in different versions.
• DOM engines as implemented by different browser vendors, plus various optimizations in different versions.
• JavaScript engines as implemented by different browser vendors, plus various optimizations in different versions.

Also, whatever results you get for your web app / web page will most like not apply to a different web app / web page, due to differences in the framework used to build that site.

Bottom line is: If you are concerned about performance testing, then Selenium is the wrong answer. Selenium is a functional test library, optimized to give you the best end-user representation. Performance is a distant afterthought.

If your goal is to get your tests to run faster, your time will be better spent looking at your test structure:

• How frequently do you open/close the browser. This is often the most time consuming activity in a test.
• How often do you refresh your element cache, how often do you need to? Consider moving your elements to Page Factory model, which lazy-loads all elements for you.
• And of course the biggest speedup factor: running your tests in parallel on multiple machines.

But I think this is getting off topic (some might suggest "ranty") from your initial question.

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