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Possible memory leak – Window object retains after window.close()

See original GitHub issue

This was initally referenced here: https://github.com/tmpvar/jsdom/issues/1493#issuecomment-268248826, but I’d like to create separate topic for that (feel free to close it if necessary).

I wanted to share my findings on using window.close() created with jsdom.jsdom().defaultView. I’ve setup a basic repro with the issue: https://github.com/thymikee/jsdom-leak-repro. Hope it helps someone familiar with jsdom internals to see what’s going on.

Below code is sufficient to retain the Window object:

const jsdom = require('jsdom');
const toMB = bytes => Math.floor(bytes / 1024 / 1024);

function spawnWindow(index) {
  let document = jsdom.jsdom({ url: 'about:blank' });
  let window = document.defaultView;
  const bytes = process.memoryUsage().heapUsed;

  console.log(index, `(${toMB(bytes)} MB)`);

  window.close();
  global.gc(); // force GC to isolate the leak
}

for (let i = 0; i < 200; i++) {
  spawnWindow(i);
}

This is actual problem that we sometimes experience at Jest, here’s on of the relevant issues: https://github.com/facebook/jest/issues/1893

Issue Analytics

State:
Created 7 years ago
Reactions:4
Comments:8 (4 by maintainers)

Top GitHub Comments

5reactions

thymikeecommented, Feb 1, 2017

@domenic just to give you an update:

@romansemko’s example is closer to what happens in Jest, as we dispose environment (i.e. call window.close()) asynchronously
we don’t experience this problem on current master (it must have been something internal, but don’t know what 🤷‍♂️)
I see 2 easy possibilities on resolving this issue (if you’re able to confirm it):
1. write about this behaviour in docs (closing window directly after jsdom.jsdom())
2. change window.close to run asynchronously in the next tick

2reactions

romansemkocommented, Jan 4, 2017

The leakage only happens if jsdom.jsdom and window.close() are synchronous. If I modify your example to fire windows.close() and global.gc() asynchronously, you will see a spike in memory, which will actually drop back to normal after the gc is done. Here the modified example:

https://github.com/romansemko/jsdom-leak-repro

const jsdom = require('jsdom');
const toMB = bytes => Math.floor(bytes / 1024 / 1024);

function spawnWindow(index) {
  let document = jsdom.jsdom({ url: 'about:blank' });
  let window = document.defaultView;

  setTimeout(() => {
    try {
      const bytes = process.memoryUsage().heapUsed;
      console.log(index, `(${toMB(bytes)} MB)`);
    } catch(error) {
      console.log(index);
    }

    window.close();

    if (global.gc) {
      global.gc();
    }
  }, 0)
}

for (let i = 0; i < 200; i++) {
  spawnWindow(i);
}

There is no issue when using jsdom.env istead of jsdom.jsdom, for example, since the code is already fired asynchronously:

function spawnWindow (index) {
    jsdom.env('<html><body>Hi</body></html>', function (err, window) {
        const bytes = process.memoryUsage().heapUsed
        console.log(index, `(${toMB(bytes)} MB)`)
        window.close()
        global.gc()
    });
}

I hope this helps to find the culprit!

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