MemLab
memlab is an end-to-end testing and analysis framework for identifying JavaScript memory leaks and optimization opportunities.
Online Resources: [Website and Demo] | [Documentation] | [Meta Engineering Blog Post]
Features:
- Browser memory leak detection - Write test scenarios with the Puppeteer API, and memlab will automatically compare JavaScript heap snapshots, filter out memory leaks, and aggregate the results
- Object-oriented heap traversing API - Supports the creation of self-defined memory leak detector, and enables programmatic analysis JS heap snapshots taken from Chromium-based browsers, Node.js, Electron.js, and Hermes
- Memory CLI toolbox - Built-in toolbox and APIs for finding memory optimization opportunities (not necessarily just memory leaks)
- Memory assertions in Node.js - Enables unit tests or running node.js programs to take a heap snapshot of their own state, perform self memory checking, or write advanced memory assertions
CLI Usage
Install the CLI
npm install -g memlabFind Memory Leaks
To find memory leaks in Google Maps, you can create a
scenario file defining how
to interact with the Google Maps, let's name it test-google-maps.js:
// initial page load url: Google Maps
function url() {
return 'https://www.google.com/maps/@37.386427,-122.0428214,11z';
}
// action where we want to detect memory leaks: click the Hotels button
async function action(page) {
// puppeteer page API
await page.click('button[aria-label="Hotels"]');
}
// action where we want to go back to the step before: click clear search
async function back(page) {
// puppeteer page API
await page.click('[aria-label="Clear search"]');
}
module.exports = {action, back, url};Now run memlab with the scenario file, memlab will interact with the web page and detect memory leaks with built-in leak detectors:
memlab run --scenario test-google-maps.jsmemlab will print memory leak results showing one representative retainer trace for each cluster of leaked objects.
Retainer traces: This is the result from an example website, the retainer trace is an object reference chain from the GC root to a leaked object. The trace shows why and how a leaked object is still kept alive in memory. Breaking the reference chain means the leaked object will no longer be reachable from the GC root, and therefore can be garbage collected. By following the leak trace one step at a time, you will be able to find a reference that should be set to null (but it wasn't due to a bug).
MemLab found 46 leak(s)
--Similar leaks in this run: 4--
--Retained size of leaked objects: 8.3MB--
[Window] (native) @35847 [8.3MB]
--20 (element)---> [InternalNode] (native) @130981728 [8.3MB]
--8 (element)---> [InternalNode] (native) @130980288 [8.3MB]
--1 (element)---> [EventListener] (native) @131009888 [8.3MB]
--1 (element)---> [V8EventListener] (native) @224808192 [8.3MB]
--1 (element)---> [eventHandler] (closure) @168079 [8.3MB]
--context (internal)---> [<function scope>] (object) @181905 [8.3MB]
--bigArray (variable)---> [Array] (object) @182925 [8.3MB]
--elements (internal)---> [(object elements)] (array) @182929 [8.3MB]
...To get readable trace, the web site under test needs to serve non-minified code (or at least minified code with readable variables, function name, and property names on objects).
Alternatively, you can debug the leak by loading the heap snapshot taken by memlab (saved in $(memlab get-default-work-dir)/data/cur)
in Chrome DevTool and search for the leaked object ID (@182929).
View Retainer Trace Interactively
View memory issues detected by memlab based on a single JavaScript heap snapshot taken from Chromium, Hermes, memlab, or any node.js or Electron.js program:
memlab view-heap --snapshot <PATH TO .heapsnapshot FILE>You can optionally specify a specific heap object with the object's id: --node-id @28173 to pinpoint a specific object.
Self-defined leak detector: If you want to use a self-defined leak detector, add a leakFilter callback
(doc)
in the scenario file. leakFilter will be called for every unreleased heap
object (node) allocated by the target interaction.
function leakFilter(node, heap) {
// ... your leak detector logic
// return true to mark the node as a memory leak
};heap is the graph representation of the final JavaScript heap snapshot.
For more details, view the
doc site.
Heap Analysis and Investigation
View which object keeps growing in size during interaction in the previous run:
memlab analyze unbound-objectAnalyze pre-fetched V8/hermes .heapsnapshot files:
memlab analyze unbound-object --snapshot-dir <DIR_OF_SNAPSHOT_FILES>Use memlab analyze to view all built-in memory analyses.
For extension, view the doc site.
View retainer trace of a particular object:
memlab trace --node-id <HEAP_OBJECT_ID>Use memlab help to view all CLI commands.
APIs
Use the memlab npm package to start a E2E run in browser and detect memory leaks.
const memlab = require('memlab');
const scenario = {
// initial page load url
url: () => 'https://www.google.com/maps/@37.386427,-122.0428214,11z',
// action where we want to detect memory leaks
action: async (page) => await page.click('button[aria-label="Hotels"]'),
// action where we want to go back to the step before
back: async (page) => await page.click('[aria-label="Clear search"]'),
}
memlab.run({scenario});Memory Assertions
memlab makes it possible to enable a unit test or running node.js program to take a heap snapshot of its own state, and write advanced memory assertions:
// save as example.test.ts
import type {IHeapSnapshot, Nullable} from '@memlab/core';
import {config, takeNodeMinimalHeap} from '@memlab/core';
class TestObject {
public arr1 = [1, 2, 3];
public arr2 = ['1', '2', '3'];
}
test('memory test with heap assertion', async () => {
config.muteConsole = true; // no console output
let obj: Nullable<TestObject> = new TestObject();
// get a heap snapshot of the current program state
let heap: IHeapSnapshot = await takeNodeMinimalHeap();
// call some function that may add references to obj
rabbitHole(obj)
expect(heap.hasObjectWithClassName('TestObject')).toBe(true);
obj = null;
heap = await takeNodeMinimalHeap();
// if rabbitHole does not have any side effect that
// adds new references to obj, then obj can be GCed
expect(heap.hasObjectWithClassName('TestObject')).toBe(false);
}, 30000);For other APIs check out the API documentation.
Development
Use node version 16 or above. To build on Windows, please use Git Bash.
First build the project as follows:
npm install
npm run buildThen keep this helper script running to ensure that local changes are picked up and compiled automatically during development:
npm run devNOTE: To run the memlab cli locally, make sure to prefix the memlab command with
npx from within the memlab repo e.g. npx memlab
Run tests:
npm run testLicense
memlab is MIT licensed, as found in the LICENSE file.
Contributing
Check our contributing guide to learn about how to contribute to the project.
Code of Conduct
Check our Code Of Conduct to learn more about our contributor standards and expectations.