[BUG] `TypeError: Cannot redefine property: name` when using esbuild with `keepNames: true`, preventing VSCode extension telemetry from being sent

[bwateratmsft]

Description/Screenshot

Discovered from microsoft/vscode-containers#367 originally. Related issues:

• TypeError: Cannot redefine property: name when using esbuild with keepNames: true, preventing telemetry from being sent vscode-extension-telemetry#237
• Webpack vscode/extension-telemetry to avoid that clients need to know exclusion rules vscode-extension-telemetry#150
• This repo: [BUG] AppInsights breaks Angular SSR in Cloudflare Worker #2523
• This repo: [BUG] AppInsights breaks Angular v20.3.* local development #2643

Quoting my original issue here, but please look there for the most up-to-date:

Boring analysis: the reason it was happening was because we're using keepNames in esbuild, to make it not mangle class/function names (which we need if we want useful call stacks). Esbuild writes code into the bundle that, at load time (which is run time), tries to set the name property on the minified classes/functions to the original name.

Some of the AppInsights packages are freezing some of their stuff, which makes it impossible to set the name property. The error that was thrown (and then caught and eaten) would resemble:

TypeError: Cannot redefine property: name
at defineProperty (<anonymous>)
at __name (d:\\vscode-containers\\dist\\extension.bundle.js:8:33)
at node_modules/@microsoft/1ds-core-js/dist-es5/AppInsightsCore.js (d:\\vscode-containers\\dist\\extension.bundle.js:16157:5)
at __init (d:\\vscode-containers\\dist\\extension.bundle.js:10:56)
at node_modules/@microsoft/1ds-core-js/dist-es5/Index.js (d:\\vscode-containers\\dist\\extension.bundle.js:16819:5)
at __init (d:\\vscode-containers\\dist\\extension.bundle.js:10:56)
at d:\\vscode-containers\\dist\\extension.bundle.js:20303:57
at async getAICore (d:\\vscode-containers\\dist\\extension.bundle.js:20303:21)
at async oneDataSystemClientFactory (d:\\vscode-containers\\dist\\extension.bundle.js:20343:29)

The end result was that loading the AppInsights packages failed silently, and the AppInsights reporter never got built--so when we logged telemetry events, they were just screamed into the void.

I considered three options. The first was to build the extension as ESM, but unfortunately this just didn't work at all.

The second was to turn off keepNames...but that would negatively impact both telemetry and the issue reporter by giving us mangled names that we would have to translate after-the-fact if we wanted to investigate.

The third was Opus' idea (nice job AI!). Basically, we build the @vscode/extension-telemetry package into its own bundle, with keepNames off, and then build everything else (extension and other dependencies) into the main bundle, with an alias to rewrite imports to @vscode/extension-telemetry to point to the other bundle.

Steps to Reproduce

1. Clone and npm install from https://github.com/microsoft/vscode-containers/tree/v2.4.0
2. In launch.json, change DEBUGTELEMETRY env var to 0
3. F5 and do anything in the Container Tools extension

• OS/Browser: Any OS
• SDK Version [e.g. 22]: (Below)
• How you initialized the SDK:
  @vscode/extension-telemetry@0.9.9
@microsoft/1ds-core-js@4.3.10
@microsoft/1ds-post-js@4.3.10
@microsoft/applicationinsights-web-basic@3.3.10

Expected behavior
Works with ESBuild without issues

[MSNev]

angular/angular-cli#31198

[bwateratmsft]

angular/angular-cli#31198

In our case this is esbuild for VSCode extensions--no Angular involved.

[bwateratmsft]

(That said, I understand if you don't want to fix this here--I wanted to open the issue either way, so that others who encounter this can see how I solved it: microsoft/vscode-azuretools#2179)

If you know any other approaches, let me know!

[MSNev]

The repro is listing v4.3.4 (published Oct 30th, 2024), have you tried using the latest version v3.3.11 (published Jan 12th, 2026)?

While we won't be "unfreezing" our built-in default Config (the only code we "freeze") there have been a couple of fixes that might affect this issue and as mentioned in the related issues we actually don't set the "name" directly.

• Fix TypeScript compatibility issue with ITelemetryPlugin interface #2597 (this is generally a TypeScript compile issue, which is unlikely to affect this -- but it is a fix that you should get) -- This fix was published in v3.3.10 (published Sept 22nd, 2025)
• add negative isArray check to _isConfigDefaults #2530 (this code is used to "copy" the frozen defaults to the mutable (unfrozen) config) -- This fix was published in v3.3.8 (published May 22nd, 2025)

[bwateratmsft]

I just checked the lockfile and we actually had @microsoft/applicationinsights-web-basic@3.3.10, along with @microsoft/1ds-core-js@4.3.10 and @microsoft/1ds-post-js@4.3.10. I updated the issue description.

Still, I'll try out the latest of those packages to make sure.

[bwateratmsft]

Ok, tried out 4.3.11 / 3.3.11 and unfortunately same issue. I'll go forward with our workaround from microsoft/vscode-azuretools#2179.

[MSNev]

Ok, I had an additional thought about this over the weekend and as part of the dynamic configuration it "requires" that the names of the configuration properties are as defined, if there is a bundler that minifies the configuration properties this is VERY likely to break something.
eg. If it's inconsistent between bundles (because extensions can be loaded after initialization and from different bundles) or we have a mechanism to enable remote enable / disabling of features or updating of configs during runtime -- this REQUIRES that the configuration properties are as expected because it just downloads a Json file and "merges" the result into the config based on the expected properties...

I'll have to do some research on how to block this, but how does vs-code handle the "keepName" false today?

[bwateratmsft]

VSCode's extension host doesn't really care if you use keepNames: false, but for us it's helpful to keep the class/function names at least in our own code. Our telemetry and issue reporters will include call stacks sometimes, and having those call stacks in cleartext makes them easier to read. Source maps could be used to decode mangled names, but that's an annoying extra step.

ESBuild is doing the actual bundling and should correctly rewrite consumers of those renamed properties as well as the properties themselves.

EDIT: Oh, now I see what you mean--the JSON is getting merged into the object but the JSON won't be minified.