Read response.json() multiple times
I'm filtering the requests/responses made by my web application using a wrapper around page.waitForRequest that reads response.json(). However when returning the matching request, when I call response.json(), I only get {}, which wouldn't match the original filter criteria.
My theory is that calling response.json() is destructive, thus can't be called twice. Could this be the case? What options would I have to avoid this kind of problem when using waitForRequest?
This thread is trying to answer question "Is calling `response.json()` destructive and can it be called twice? How can this problem be avoided when using `waitForRequest`?"
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Answer
Working with response.json() in Playwright
In Playwright, response.json() is a method that extracts the JSON body from a response object. It's not destructive and can be called multiple times without any issues. Each time you call it, it parses the response body again and returns a new promise with the parsed JSON data.
Here are a couple of best practices to follow when using response.json():
Store the Result in a Variable
To avoid making multiple calls to response.json(), store its result in a variable and reuse it. This improves performance. Here's how you can do it:
const jsonResponse = await response.json();
// Now, you can use jsonResponse wherever neededHandle Errors Gracefully
When working with asynchronous operations like parsing JSON, it's crucial to handle errors properly. Use try-catch blocks or .catch() methods on promises. This ensures that if an error occurs during parsing, your code doesn't break and allows for appropriate error handling.
try {
const jsonResponse = await response.json();
// Use jsonResponse wherever needed
} catch (error) {
// Handle error gracefully
}By following these practices, you can safely use response.json() multiple times without encountering any issues or unexpected behavior when using Playwright's waitForResponse function. For more tips on efficient Playwright test scripts, check out this blog post.
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