139 lines
4.5 KiB
Markdown
139 lines
4.5 KiB
Markdown
# Debugging
|
|
|
|
Debugging with Puppeteer can be an arduous task. There is no _single_ method for
|
|
debugging all possible issues since Puppeteer touches many distinct components
|
|
of a browser such as network requests and Web APIs. On a high note, Puppeteer
|
|
provides _several_ methods for debugging which hopefully does cover all possible
|
|
issues.
|
|
|
|
## Background
|
|
|
|
In general, there are two possible sources of an issue: Code running on Node.js
|
|
(which we call _server code_), and
|
|
[code running in the browser](../api/puppeteer.page.evaluate)
|
|
(which we call _client code_). There is also a third possible source being the
|
|
browser itself (which we call _internal code_), but if you suspect this is the
|
|
source **after attempting the methods below**, we suggest
|
|
[searching existing issues](https://github.com/puppeteer/puppeteer/issues)
|
|
before
|
|
[filing an issue](https://github.com/puppeteer/puppeteer/issues/new/choose).
|
|
|
|
## Debugging methods for all situations
|
|
|
|
These methods can be used to debug any situation. These should be used as a
|
|
quick sanity check before diving into more complex methods.
|
|
|
|
### Turn off [`headless`](../api/puppeteer.browserlaunchargumentoptions)
|
|
|
|
Sometimes it's useful to see what the browser is displaying. Instead of
|
|
launching in
|
|
[`headless`](../api/puppeteer.browserlaunchargumentoptions) mode,
|
|
launch a full version of the browser with
|
|
[`headless`](../api/puppeteer.browserlaunchargumentoptions) set to
|
|
`false`:
|
|
|
|
```ts
|
|
const browser = await puppeteer.launch({headless: false});
|
|
```
|
|
|
|
### Puppeteer "slow-mo"
|
|
|
|
The [`slowMo`](../api/puppeteer.browserconnectoptions) option slows down
|
|
Puppeteer operations by a specified amount of milliseconds. It's another way to
|
|
help see what's going on.
|
|
|
|
```ts
|
|
const browser = await puppeteer.launch({
|
|
headless: false,
|
|
slowMo: 250, // slow down by 250ms
|
|
});
|
|
```
|
|
|
|
## Debugging methods for client code
|
|
|
|
### Capture `console.*` output
|
|
|
|
Since client code runs in the browser, doing `console.*` in client code will not
|
|
directly log to Node.js. However, you can [listen](../api/puppeteer.page.on) for
|
|
the [`console`](../api/puppeteer.pageeventobject) event which returns a
|
|
payload with the logged text.
|
|
|
|
```ts
|
|
page.on('console', msg => console.log('PAGE LOG:', msg.text()));
|
|
|
|
await page.evaluate(() => console.log(`url is ${location.href}`));
|
|
```
|
|
|
|
### Use the debugger in the browser
|
|
|
|
1. Set [`devtools`](../api/puppeteer.browserlaunchargumentoptions) to
|
|
`true` when launching Puppeteer:
|
|
|
|
```ts
|
|
const browser = await puppeteer.launch({devtools: true});
|
|
```
|
|
|
|
2. Add `debugger` inside any client code you want debugged. For example,
|
|
|
|
```ts
|
|
await page.evaluate(() => {
|
|
debugger;
|
|
});
|
|
```
|
|
|
|
The Browser will now stop in the location the `debugger` word is found in
|
|
debug mode.
|
|
|
|
## Debugging methods for server code
|
|
|
|
### Use the debugger in Node.js (Chrome/Chromium-only)
|
|
|
|
Since server code intermingles with client code, this method of debugging is
|
|
closely tied with the browser. For example, you can step over
|
|
`await page.click()` in the server script and see the click happen in the
|
|
browser.
|
|
|
|
Note that you won't be able to run `await page.click()` in DevTools console due
|
|
to this
|
|
[Chromium bug](https://bugs.chromium.org/p/chromium/issues/detail?id=833928), so
|
|
if you want to try something out, you have to add it to your test file.
|
|
|
|
1. Set [`headless`](../api/puppeteer.browserlaunchargumentoptions) to
|
|
`false`.
|
|
2. Add `debugger` to any server code you want debugged. For example,
|
|
|
|
```ts
|
|
debugger;
|
|
await page.click('a[target=_blank]');
|
|
```
|
|
|
|
3. Run your server code with `--inspect-brk`. For example,
|
|
|
|
```sh
|
|
node --inspect-brk path/to/script.js
|
|
```
|
|
|
|
4. In the opened Chrome/Chromium browser, open `chrome://inspect/#devices` and
|
|
click `inspect`.
|
|
5. In the newly opened test browser, press `F8` to resume test execution.
|
|
6. Now your `debugger` statement will be hit and you can debug in the test
|
|
browser.
|
|
|
|
### Log DevTools protocol traffic
|
|
|
|
If all else fails, it's possible there may be an issue between Puppeteer and the
|
|
DevTools protocol. You can debug this by setting the `DEBUG` environment
|
|
variable before running your script. This will log internal traffic via
|
|
[`debug`](https://github.com/visionmedia/debug) under the `puppeteer` namespace.
|
|
|
|
```sh
|
|
# Basic verbose logging
|
|
env DEBUG="puppeteer:*" node script.js
|
|
|
|
# Prevent truncating of long messages
|
|
env DEBUG="puppeteer:*" env DEBUG_MAX_STRING_LENGTH=null node script.js
|
|
|
|
# Protocol traffic can be rather noisy. This example filters out all Network domain messages
|
|
env DEBUG="puppeteer:*" env DEBUG_COLORS=true node script.js 2>&1 | grep -v '"Network'
|
|
```
|