Importing from Node.js

Jamie Wong edited this page Oct 8, 2018 · 4 revisions

There are two ways to import profiles from Node.js: using the Chrome inspector, and using node --prof. The Chrome inspector strategy can also be used to import heap snapshots.

Importing from the Chrome inspector

Node now has built-in support to be inspected using Chrome. This article by Paul Irish has more details.

Run your program with --inspect. For example, this is how you'd profile a build of parcel

node --inspect node_modules/.bin/parcel assets/index.html

Now visit chrome://inspect, and you should see something like this:

chrome://inspect page

Click the "inspect" link. This should open a developer tools window.

Clicking the start button

Click the start button to start recording a profile.

Clicking the stop button

Now force the node behavior you're trying to profile (e.g. by loading the webpage it serves). When you're done, click the stop button.

Clicking on "save"

Click on "save" to save the recorded profile. Save it with the default .cpuprofile file extension.

Saving the ".cpuprofile" file

You should be able to open that file in https://www.speedscope.app/.

To view it offline, you'll need to install speedscope via npm:

npm install -g speedscope

Then you should be able to open it like so:

speedscope /path/to/profile.json

Importing a heap profile

Like the CPU Profiling, you can use the Chrome Inspector to record a heap allocation profile. First, launch your process with the --inspect flag. Next, go the Memory section and select the "Allocation sampling" option.

Selection allocation sampling

Click the start button to start recording a profile.

Now, use the application for a while, then click the Stop button.

Saving the .heapprofile file

Click "save" to save the recorded profile. Save it with the default .heapprofile file extension.

You should be able to open that file in https://www.speedscope.app/.

To view it offline, you'll need to install speedscope via npm:

npm install -g speedscope

Then you should be able to open it like so:

speedscope /path/to/profile.heapprofile

Importing from node --prof

If you record profiling information like so:

node --prof /path/to/my/script.js

Then this will generate one or more isolate*.log files. You can convert these files into a file that can be imported into speedscope like so:

node --prof-process --preprocess -j isolate*.log > profile.v8log.json

You should be able to open that file in https://www.speedscope.app/.

To view it offline, you'll need to install speedscope via npm:

npm install -g speedscope

Then you should be able to open it like so:

speedscope /path/to/profile.v8log.json

You can also pipe the output of node --prof-process directly to speedscope with a trailing - like so:

node --prof-process --preprocess -j isolate*.log | speedscope -
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