The util.deprecate() method wraps fn (which may be a function or class) in such a way that it is marked as deprecated.

const util = require('node:util');

exports.obsoleteFunction = util.deprecate(() => {
  // Do something here.
}, 'obsoleteFunction() is deprecated. Use newShinyFunction() instead.');

When called, util.deprecate() will return a function that will emit aDeprecationWarning using the 'warning' event. The warning will be emitted and printed to stderr the first time the returned function is called. After the warning is emitted, the wrapped function is called without emitting a warning.

If the same optional code is supplied in multiple calls to util.deprecate(), the warning will be emitted only once for that code.

const util = require('node:util');

const fn1 = util.deprecate(someFunction, someMessage, 'DEP0001');
const fn2 = util.deprecate(someOtherFunction, someOtherMessage, 'DEP0001');
fn1(); // Emits a deprecation warning with code DEP0001
fn2(); // Does not emit a deprecation warning because it has the same code

If either the --no-deprecation or --no-warnings command-line flags are used, or if the process.noDeprecation property is set to true_prior_ to the first deprecation warning, the util.deprecate() method does nothing.

If the --trace-deprecation or --trace-warnings command-line flags are set, or the process.traceDeprecation property is set to true, a warning and a stack trace are printed to stderr the first time the deprecated function is called.

If the --throw-deprecation command-line flag is set, or theprocess.throwDeprecation property is set to true, then an exception will be thrown when the deprecated function is called.

The --throw-deprecation command-line flag and process.throwDeprecationproperty take precedence over --trace-deprecation andprocess.traceDeprecation.