While waiting for a permanent solution, you can disable it yourself:

1. undock devtools
2. invoke devtools-for-devtools by pressing Ctrl-Shift-I
3. run the following code:
   ObjectUI.JavaScriptAutocomplete.completionsForTextInCurrentContext = () => Promise.resolve([]);
4. close devtools-for-devtools

Notes:
* By default this will limit autocomplete to your own typed commands
  (may be also disabled via devtools -> settings -> console -> autocomplete from history).
* Naturally, this will work only until the main devtools is closed.
  You can patch resources.pak in the browser installation directory, though.
* after undocking was selected once you can quickly perform everything via keyboard:
  Ctrl-Shift-I, Ctrl-Shift-D, Ctrl ~ and other keys would helpful.

Thanks woxxom@ for the workaround.

ruththompson@: Could you please attach any sample app to test and confirm this also, please confirm if the workaround suggested above works for you.

@woxxom Thank you so much for that workaround, yes it works!

@divyapadigela, I'll see if I can throw an example together soon. I don't have time to do it this week.

Thank you for providing more feedback. Adding requester "divya.padigela@techmahindra.com" to the cc list and removing "Needs-Feedback" label.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Do we need to fetch only the viewport rows to support this use case?

FWIW, a simple repro:
1. open a new tab page
2. open devtools (Ctrl-Shift-I key)
3. paste and run the following code:
   for (var i = 0; i < 200e3; i++) window['var' + i] = true
4. type the following:
   var123

Expected: able to type without delays
Observed: several second delay after typing each letter depending on CPU speed

Just kidding, here is an example:

Deleted: DebuggerExampleApp.html 911 bytes

DebuggerExampleApp.html 911 bytes View Download

oh.  Yes, same as woxxom's repro.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d5ed67e13e9939c00aed1876e8701cb47101cf6f

commit d5ed67e13e9939c00aed1876e8701cb47101cf6f
Author: Joel Einbinder <einbinder@chromium.org>
Date: Tue Dec 19 01:53:13 2017

DevTools: Make console autocomplete faster

This introduces caching of autocompletions, small tweaks to increase
performance, and converts JavaScriptAutocomplete into a singleton
instead of a set of functions.

Bug:  784678 
Change-Id: Iacdcd9d3a884f0377266663cdeb3d8cce48d72d1
Reviewed-on: https://chromium-review.googlesource.com/770254
Commit-Queue: Joel Einbinder <einbinder@chromium.org>
Reviewed-by: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524902}
[modify] https://crrev.com/d5ed67e13e9939c00aed1876e8701cb47101cf6f/third_party/WebKit/LayoutTests/http/tests/devtools/console-cd-completions.js
[modify] https://crrev.com/d5ed67e13e9939c00aed1876e8701cb47101cf6f/third_party/WebKit/LayoutTests/http/tests/devtools/console-completions.js
[modify] https://crrev.com/d5ed67e13e9939c00aed1876e8701cb47101cf6f/third_party/WebKit/LayoutTests/http/tests/devtools/sources/debugger/debugger-completions-on-call-frame.js
[modify] https://crrev.com/d5ed67e13e9939c00aed1876e8701cb47101cf6f/third_party/WebKit/Source/devtools/front_end/console/ConsolePrompt.js
[modify] https://crrev.com/d5ed67e13e9939c00aed1876e8701cb47101cf6f/third_party/WebKit/Source/devtools/front_end/object_ui/JavaScriptAutocomplete.js
[modify] https://crrev.com/d5ed67e13e9939c00aed1876e8701cb47101cf6f/third_party/WebKit/Source/devtools/front_end/object_ui/ObjectPropertiesSection.js

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e0c6ec427c2d94c785d1b4e6ac16bd4dbd1d6ad1

commit e0c6ec427c2d94c785d1b4e6ac16bd4dbd1d6ad1
Author: Joel Einbinder <einbinder@chromium.org>
Date: Mon Feb 12 22:42:10 2018

DevTools: Limit autocomplete items to 10000 per prototype

Bug:  784678 
Change-Id: If8d0eb1a6eb9488133917f3c275f64cd2405bd73
Reviewed-on: https://chromium-review.googlesource.com/914806
Reviewed-by: Pavel Feldman <pfeldman@chromium.org>
Commit-Queue: Joel Einbinder <einbinder@chromium.org>
Cr-Commit-Position: refs/heads/master@{#536220}
[modify] https://crrev.com/e0c6ec427c2d94c785d1b4e6ac16bd4dbd1d6ad1/third_party/WebKit/Source/devtools/front_end/object_ui/JavaScriptAutocomplete.js

Verified this issue on Debian Rodete with chrome #66.0.3346.0 and observed fix is working as expected, didn't observe any lags with provided code in comment #8,#9. hence adding TE-Verified labels.

Attaching the screen-cast for reference.

Deleted: 784678.mp4 785 KB

	784678.mp4 785 KB View Download

There's nothing Google-specific here, so trying to make the bug public (since I see access is causing some confusion).

It looks like there's been some significant improvements here in Chrome 66.   ruththompson@ can you try Chrome beta and tell us what you think?

Sorry, scratch that - I've done what I should have done first and try the demo above myself, and it's still extremely laggy on a fast machine despite the 10,000 limit (which I assume was likely to make things a lot better).

einbinder@ any other ideas?  Is the 10,000 item limit actually working?  Does it need to be even lower?

I'm leaving this open until the patches hit stable, because we will only really know if things are fixed once developers are using the new autocomplete daily. But everything should be working in 66 (beta). 

This has been in stable for awhile now, should we call this bug fixed?  I've pinged GMail folks to ask again, but feel free to resolve Fixed regardless as long as we're not aware of remaining issues here.

GMail team says that they "verified that autocomplete is now working very well".  Let's call this fixed.