The process.allowedNodeEnvironmentFlags property is a special, read-only Set of flags allowable within the NODE_OPTIONS environment variable.

process.allowedNodeEnvironmentFlags extends Set, but overridesSet.prototype.has to recognize several different possible flag representations. process.allowedNodeEnvironmentFlags.has() will return true in the following cases:

• Flags may omit leading single (-) or double (--) dashes; e.g.,inspect-brk for --inspect-brk, or r for -r.
• Flags passed through to V8 (as listed in --v8-options) may replace one or more non-leading dashes for an underscore, or vice-versa; e.g., --perf_basic_prof, --perf-basic-prof, --perf_basic-prof, etc.
• Flags may contain one or more equals (=) characters; all characters after and including the first equals will be ignored; e.g., --stack-trace-limit=100.
• Flags must be allowable within NODE_OPTIONS.

When iterating over process.allowedNodeEnvironmentFlags, flags will appear only once; each will begin with one or more dashes. Flags passed through to V8 will contain underscores instead of non-leading dashes:

import { allowedNodeEnvironmentFlags } from 'node:process';

allowedNodeEnvironmentFlags.forEach((flag) => {
  // -r
  // --inspect-brk
  // --abort_on_uncaught_exception
  // ...
});

The methods add(), clear(), and delete() ofprocess.allowedNodeEnvironmentFlags do nothing, and will fail silently.

If Node.js was compiled without NODE_OPTIONS support (shown in config), process.allowedNodeEnvironmentFlags will contain what would have been allowable.