One of the most fundamental techniques to learn when using WebDriver is how to find elements on the page. WebDriver offers a number of built-in selector types, amongst them finding an element by its ID attribute:
WebElement cheese = driver.findElement(By.id("cheese"));
IWebElement element = driver.FindElement(By.Id("cheese"));
cheese = driver.find_element(id: 'cheese')
const cheese = driver.findElement(By.id('cheese'));
val cheese: WebElement = driver.findElement(By.id("cheese"))
As seen in the example, locating elements in WebDriver is done on the
WebDriver instance object. The
findElement(By) method returns
another fundamental object type, the
WebDriverrepresents the browser
WebElementrepresents a particular DOM node (a control, e.g. a link or input field, etc.)
Once you have a reference to a web element that’s been “found”, you can narrow the scope of your search by using the same call on that object instance:
WebElement cheese = driver.findElement(By.id("cheese")); WebElement cheddar = cheese.findElement(By.id("cheddar"));
cheese = driver.find_element_by_id("cheese") cheddar = cheese.find_elements_by_id("cheddar")
IWebElement cheese = driver.FindElement(By.Id("cheese")); IWebElement cheddar = cheese.FindElement(By.Id("cheddar"));
cheese = driver.find_element(id: 'cheese') cheddar = cheese.find_element(id: 'cheddar')
const cheese = driver.findElement(By.id('cheese')); const cheddar = cheese.findElement(By.id('cheddar'));
val cheese = driver.findElement(By.id("cheese")) val cheddar = cheese.findElement(By.id("cheddar"))
You can do this because both the WebDriver and WebElement types implement the SearchContext interface. In WebDriver, this is known as a role-based interface. Role-based interfaces allow you to determine whether a particular driver implementation supports a given feature. These interfaces are clearly defined and try to adhere to having only a single role of responsibility. You can read more about WebDriver’s design and what roles are supported in which drivers in the Some Other Section Which Must Be Named.
Consequently, the By interface used above also supports a number of additional locator strategies. A nested lookup might not be the most effective cheese location strategy since it requires two separate commands to be issued to the browser; first searching the DOM for an element with ID “cheese”, then a search for “cheddar” in a narrowed context.
To improve the performance slightly, we should try to use a more specific locator: WebDriver supports looking up elements by CSS locators, allowing us to combine the two previous locators into one search:
cheddar = driver.find_element_by_css_selector("#cheese #cheddar")
driver.find_element(css: '#cheese #cheddar')
const cheddar = driver.findElement(By.css('#cheese #cheddar'));
It is possible that the document we are working with may turn out to have an ordered list of the cheese we like the best:
<ol id=cheese> <li id=cheddar>… <li id=brie>… <li id=rochefort>… <li id=camembert>… </ul>
Since more cheese is undisputably better, and it would be cumbersome
to have to retrieve each of the items individually, a superior
technique for retrieving cheese is to make use of the pluralized
findElements(By). This method returns a collection of web
elements. If only one element is found, it will still return a
collection (of one element). If no element matches the locator, an
empty list will be returned.
List<WebElement> muchoCheese = driver.findElements(By.cssSelector("#cheese li"));
mucho_cheese = driver.find_elements_by_css_selector("#cheese li")
IReadOnlyList<IWebElement> muchoCheese = driver.FindElements(By.CssSelector(“#cheese li”));
mucho_cheese = driver.find_elements(css: '#cheese li')
const muchoCheese = driver.findElements(By.css('#cheese li'));
val muchoCheese: List<WebElement> = driver.findElements(By.cssSelector("#cheese li"))
There are eight different built-in element location strategies in WebDriver:
|class name||Locates elements whose class name contains the search value (compound class names are not permitted)|
|css selector||Locates elements matching a CSS selector|
|id||Locates elements whose ID attribute matches the search value|
|name||Locates elements whose NAME attribute matches the search value|
|link text||Locates anchor elements whose visible text matches the search value|
|partial link text||Locates anchor elements whose visible text contains the search value. If multiple elements are matching, only the first one will be selected.|
|tag name||Locates elements whose tag name matches the search value|
|xpath||Locates elements matching an XPath expression|
In general, if HTML IDs are available, unique, and consistently predictable, they are the preferred method for locating an element on a page. They tend to work very quickly, and forego much processing that comes with complicated DOM traversals.
If unique IDs are unavailable, a well-written CSS selector is the preferred method of locating an element. XPath works as well as CSS selectors, but the syntax is complicated and frequently difficult to debug. Though XPath selectors are very flexible, they are typically not performance tested by browser vendors and tend to be quite slow.
Selection strategies based on link text and partial link text have drawbacks in that they only work on link elements. Additionally, they call down to XPath selectors internally in WebDriver.
Tag name can be a dangerous way to locate elements. There are frequently multiple elements of the same tag present on the page. This is mostly useful when calling the findElements(By) method which returns a collection of elements.
The recommendation is to keep your locators as compact and readable as possible. Asking WebDriver to traverse the DOM structure is an expensive operation, and the more you can narrow the scope of your search, the better.