Inspector is already activated
Production Risk
Low — the inspector should not be opened in production code.
Thrown when inspector.open() is called but the inspector is already active. The Node.js inspector can only be opened once per process; calling open() again while it is already listening is not permitted.
- 1Calling inspector.open() more than once without calling inspector.close() first
- 2Multiple modules or plugins both trying to open the inspector
Triggered when inspector.open() is called on an already-active inspector session.
const inspector = require('inspector');
inspector.open(9229);
inspector.open(9229); // already active — throwsexpected output
Error [ERR_INSPECTOR_ALREADY_ACTIVATED]: Inspector is already activated
Fix
Check if the inspector is open before calling open()
WHEN When multiple code paths may try to open the inspector
const inspector = require('inspector');
if (!inspector.url()) { // url() returns undefined if not open
inspector.open(9229, 'localhost', false);
}Why this works
inspector.url() returns the WebSocket URL if active; checking it prevents duplicate opens.
const inspector = require('inspector');
inspector.open(9229);
inspector.open(9229); // already active — throws // this triggers ERR_INSPECTOR_ALREADY_ACTIVATEDtry {
// operation that may throw ERR_INSPECTOR_ALREADY_ACTIVATED
riskyOperation()
} catch (err) {
if (err.code === 'ERR_INSPECTOR_ALREADY_ACTIVATED') {
console.error('ERR_INSPECTOR_ALREADY_ACTIVATED:', err.message)
} else {
throw err
}
}// Validate inputs before calling the operation
function safe_err_inspector_already_activated(...args) {
// validate args here
return performOperation(...args)
}✕ Call inspector.open() unconditionally multiple times
The inspector is a singleton per process; re-opening without closing throws.
Node.js Error Codes Documentation
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