为什么这两个元素定位器调用的行为不同？

Question

I am writing webdriver automation using JavaScript to test a web app. I have code that looks like this:

var selenium = require('selenium-webdriver');
By = selenium.By;
until = selenium.until;

driver = new selenium.Builder().
  withCapabilities(selenium.Capabilities.chrome()).
  build();

getItems = async function() {
  try {
    var itemsXpath = '[xpath expression]';
    var items = await driver.findElements(By.xpath(itemsXpath));
    console.log(items.length + ' items found');
    ...
  }
  catch(err) {
    console.log(err);
  }
}

This succeeds. However, if I replace the await line with:

var items = await driver.wait(until.elementsLocated(By.xpath(itemsXpath)),60000);

it does not execute as expected. Neither the following console.log() , nor the one in the catch() block, are displayed.

From reading the documentation , my impression was that if there were items on the page which match the XPath locator, either of these functions would work, and return the elements. However, if the elements were not on the page, the second formulation would wait for them to appear (up to 60000 ms, in this case).

Note that the second way of writing this does not work, even if the items are already on the screen at the time getItems() is called. Also, the program is completing in less time than the timeout specified in driver.wait() .

Is there something I have misunderstood about how this works, such that this behavior actually makes sense? If so, can anyone clarify what is going on here?

Answer 1

The line you have written:

var items = await driver.findElements(By.xpath(itemsXpath));

will check for the element and returns Array<WebElement> if the given xpath matches with any element(s).

But the wait methods what you used:

var items = await driver.wait(until.elementsLocated(By.xpath(itemsXpath)),60000);

will not return any element. It simply waits until the element is located in the DOM.

Anyhow, you have specified 60 seconds to find the element using elementLocated method. This line will wait a maximum of 60 seconds to find an element matching with your xpath. If the specified xpath matches with any element in less than 60 seconds, it will simply end that wait on that particular time and move to the next line. Note that there won't be any error in such situations. Hence, there is no chance of going to catch block.

You can refer to this page for more details on this.