Playwright Event Handling Introduction
In the past, a common way to wait for a specific event in test automation was to use a polling loop. This involved repeatedly checking the page until the event occurred. However, this approach could be time-consuming and inefficient, especially if the event was rare or unpredictable.
Another approach was to use a sleep statement, which would pause the script for a specified amount of time, giving the event a chance to occur. However, this could also be inefficient if the event did not occur within the specified time period.
In addition to the challenges of waiting for events, controlling the browser posed challenges. In the early days of automation, there were no standardized APIs for controlling browsers. This meant that testers had to write custom code for each browser they wanted to automate, which was a time-consuming and error-prone process.
Today, test automation tools have become much more sophisticated. They offer features like event listening and browser control that were not available in the early days. This has made test automation much easier and more efficient.
Playwright can listen to webpage events, which is useful when waiting for a specific event before proceeding with the script. For instance, if you need to wait for a response before clicking on a UI element and there is a race condition between clicking and waiting for a response, listening to events can ensure consistent and successful test results.
The waitForResponse() The function returns the matched response. It accepts a Request URL as a string, a regex, or a predicate that receives a Response object. If baseURL is provided and the URL is a path, it's merged with new URL() the constructor.
page.waitForResponse('<https://example.com/resource>');
page.waitForResponse(response => response.url() === '[<https://example.com>](<https://example.com/>)' && response.status() === 200);
page.waitForResponse('/resource')To avoid a race condition when clicking and waiting for a response, use an asynchronous function that returns the response from a Promise.all() method. This method allows you to wait for the results of multiple promises before continuing with the code. As a result, it is useful for tasks that require the results of several asynchronous operations.
Create a waitAndClick() function with three arguments to replace the direct use of waitForResponse(). This ensures that the button is clicked only after the API response is received, reducing the risk of flaky test results.
page: The Page object that represents the current browser window.locator: hat identifies the element to click.url: The URL of the server that will respond to the click event.
export async function waitAndClick(page: Page, locator: string, url: string) {
const [response] = await Promise.all([
page.waitForResponse(url),
page.click(locator)
]);
return response;
}If you are unsure about the URL you are awaiting, use the code snippet below to intercept all network requests made by the page and log the URL of each request to the console.
await page.route('**', route => {
console.log(route.request().url());
route.continue();
})The page.route() method takes a regular expression as its first argument, where ** matches all URLs. The second argument to the method is a callback function that will be called for each intercepted request. The function will receive a parameter of type Route, which contains information about the intercepted request, such as the URL, method, and headers.
In the callback function, you can log the URL of the request to the console using the route.request().url() method. You can also use the route.continue() method to allow the request to proceed as normal.
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