process.emitWarning

History

process.emitWarning(warning, options?): void

Attributes

warning:string | Error

The warning to emit.

options:Object

type?:string

When warning is a String, type is the name to use for the type of warning being emitted. Default: 'Warning'.

code:string

A unique identifier for the warning instance being emitted.

ctor?:Function

When warning is a String, ctor is an optional function used to limit the generated stack trace. Default: process.emitWarning.

detail:string

Additional text to include with the error.

The process.emitWarning() method can be used to emit custom or application specific process warnings. These can be listened for by adding a handler to the 'warning' event.

import { emitWarning } from 'node:process';

// Emit a warning with a code and additional detail.
emitWarning('Something happened!', {
  code: 'MY_WARNING',
  detail: 'This is some additional information',
});
// Emits:
// (node:56338) [MY_WARNING] Warning: Something happened!
// This is some additional information

JavaScript

const { emitWarning } = require('node:process');

// Emit a warning with a code and additional detail.
emitWarning('Something happened!', {
  code: 'MY_WARNING',
  detail: 'This is some additional information',
});
// Emits:
// (node:56338) [MY_WARNING] Warning: Something happened!
// This is some additional information

JavaScript

In this example, an Error object is generated internally by process.emitWarning() and passed through to the 'warning' handler.

import process from 'node:process';

process.on('warning', (warning) => {
  console.warn(warning.name);    // 'Warning'
  console.warn(warning.message); // 'Something happened!'
  console.warn(warning.code);    // 'MY_WARNING'
  console.warn(warning.stack);   // Stack trace
  console.warn(warning.detail);  // 'This is some additional information'
});

JavaScript

process.on('warning', (warning) => {
  console.warn(warning.name);    // 'Warning'
  console.warn(warning.message); // 'Something happened!'
  console.warn(warning.code);    // 'MY_WARNING'
  console.warn(warning.stack);   // Stack trace
  console.warn(warning.detail);  // 'This is some additional information'
});

JavaScript

If warning is passed as an Error object, the options argument is ignored.