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feat: add diagnostics_channel support for app initialization #7041

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feat: add diagnostics_channel support for app initialization #7041

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b7d982e
feat: add diagnostics_channel support for app initialization
DemianParkhomenko Feb 18, 2026
73207d4
Fix contract of diagnostics channel publish
DemianParkhomenko Feb 20, 2026
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7 changes: 7 additions & 0 deletions lib/diagnostics.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,7 @@
'use strict';

const dc = require('node:diagnostics_channel');

const initialization = dc.channel('express.initialization');
Comment on lines +3 to +5
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Copilot AI Feb 20, 2026

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The codebase convention for top-level requires in lib/ files is to use var rather than const. This pattern is consistently followed across all other lib/ files (application.js, request.js, response.js, utils.js, view.js, express.js). While const is used in the codebase for destructuring and local variables inside functions, top-level requires should use var for consistency with the rest of the codebase.

Suggested change
const dc = require('node:diagnostics_channel');
const initialization = dc.channel('express.initialization');
var dc = require('node:diagnostics_channel');
var initialization = dc.channel('express.initialization');

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module.exports = { initialization };
6 changes: 6 additions & 0 deletions lib/express.js
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Expand Up @@ -19,6 +19,7 @@ var proto = require('./application');
var Router = require('router');
var req = require('./request');
var res = require('./response');
const channels = require('./diagnostics');
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Copilot AI Feb 20, 2026

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The codebase convention for top-level requires in lib/ files is to use var rather than const. All other module requires in this file (lines 15-21) use var, and this pattern is consistently followed across all other lib/ files (application.js, request.js, response.js, utils.js, view.js). While const is used in the codebase for destructuring and local variables inside functions, top-level requires should use var for consistency.

Suggested change
const channels = require('./diagnostics');
var channels = require('./diagnostics');

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/**
* Expose `createApplication()`.
Expand Down Expand Up @@ -52,6 +53,11 @@ function createApplication() {
})

app.init();

if (channels.initialization.hasSubscribers) {
channels.initialization.publish({ app });
}

return app;
}

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26 changes: 26 additions & 0 deletions test/diagnostics-channel.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,26 @@
'use strict'

const dc = require('node:diagnostics_channel')
const express = require('../')
const assert = require('node:assert')

describe('diagnostics channels', function () {
describe('express.initialization', function () {
it('should publish when app is created', function () {
let msg

dc.subscribe('express.initialization', function handler (data) {
msg = data
dc.unsubscribe('express.initialization', handler)
})

const app = express()
assert.ok(msg, 'express.initialization was not published')
assert.strictEqual(msg.app, app)
})

it('should not throw when there are no subscribers', function () {
assert.ok(express())
})
})
})
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