method Process.emitWarning
Usage in Deno
import { type Process } from "node:process";
Process.emitWarning(warning: string | Error,ctor?: Function,): void
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 using a string.
emitWarning('Something happened!');
// Emits: (node: 56338) Warning: Something happened!
import { emitWarning } from 'node:process';
// Emit a warning using a string and a type.
emitWarning('Something Happened!', 'CustomWarning');
// Emits: (node:56338) CustomWarning: Something Happened!
import { emitWarning } from 'node:process';
emitWarning('Something happened!', 'CustomWarning', 'WARN001');
// Emits: (node:56338) [WARN001] CustomWarning: Something happened!
```js
In each of the previous examples, an `Error` object is generated internally by `process.emitWarning()` and passed through to the `'warning'` handler.
```js
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'
});
If warning is passed as an Error object, it will be passed through to the 'warning' event handler
unmodified (and the optional type, code and ctor arguments will be ignored):
import { emitWarning } from 'node:process';
// Emit a warning using an Error object.
const myWarning = new Error('Something happened!');
// Use the Error name property to specify the type name
myWarning.name = 'CustomWarning';
myWarning.code = 'WARN001';
emitWarning(myWarning);
// Emits: (node:56338) [WARN001] CustomWarning: Something happened!
A TypeError is thrown if warning is anything other than a string or Error object.
While process warnings use Error objects, the process warning mechanism is not a replacement for normal error handling mechanisms.
The following additional handling is implemented if the warning type is 'DeprecationWarning':
- If the
--throw-deprecationcommand-line flag is used, the deprecation warning is thrown as an exception rather than being emitted as an event. - If the
--no-deprecationcommand-line flag is used, the deprecation warning is suppressed. - If the
--trace-deprecationcommand-line flag is used, the deprecation warning is printed tostderralong with the full stack trace.
void
Process.emitWarning(warning: string | Error,options?: EmitWarningOptions,): void
optional
options: EmitWarningOptions
void