util

import { aborted } from 'node:util';

// Obtain an object with an abortable signal, like a custom resource or operation.
const dependent = obtainSomethingAbortable();

// Pass `dependent` as the resource, indicating the promise should only resolve
// if `dependent` is still in memory when the signal is aborted.
aborted(dependent.signal, dependent).then(() => {
  // This code runs when `dependent` is aborted.
  console.log('Dependent resource was aborted.');
});

// Simulate an event that triggers the abort.
dependent.on('event', () => {
  dependent.abort(); // This will cause the `aborted` promise to resolve.
});

import util from 'node:util';

async function fn() {
  return 'hello world';
}
const callbackFunction = util.callbackify(fn);

callbackFunction((err, ret) => {
  if (err) throw err;
  console.log(ret);
});

hello world

function fn() {
  return Promise.reject(null);
}
const callbackFunction = util.callbackify(fn);

callbackFunction((err, ret) => {
  // When the Promise was rejected with `null` it is wrapped with an Error and
  // the original value is stored in `reason`.
  err && Object.hasOwn(err, 'reason') && err.reason === null;  // true
});

import util from 'node:util';
const debuglog = util.debuglog('foo');

debuglog('hello from foo [%d]', 123);

FOO 3245: hello from foo [123]

import util from 'node:util';
const debuglog = util.debuglog('foo-bar');

debuglog('hi there, it\'s foo-bar [%d]', 2333);

FOO-BAR 3257: hi there, it's foo-bar [2333]

import util from 'node:util';
let debuglog = util.debuglog('internals', (debug) => {
  // Replace with a logging function that optimizes out
  // testing if the section is enabled
  debuglog = debug;
});

import util from 'node:util';

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

import util from '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

util.format('%s:%s', 'foo');
// Returns: 'foo:%s'

util.format('%s:%s', 'foo', 'bar', 'baz');
// Returns: 'foo:bar baz'

util.format(1, 2, 3);
// Returns: '1 2 3'

util.format('%% %s');
// Returns: '%% %s'

util.formatWithOptions({ colors: true }, 'See object %O', { foo: 42 });
// Returns 'See object { foo: 42 }', where `42` is colored as a number
// when printed to a terminal.

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

function exampleFunction() {
  const callSites = util.getCallSites();

  console.log('Call Sites:');
  callSites.forEach((callSite, index) => {
    console.log(`CallSite ${index + 1}:`);
    console.log(`Function Name: ${callSite.functionName}`);
    console.log(`Script Name: ${callSite.scriptName}`);
    console.log(`Line Number: ${callSite.lineNumber}`);
    console.log(`Column Number: ${callSite.column}`);
  });
  // CallSite 1:
  // Function Name: exampleFunction
  // Script Name: /home/example.js
  // Line Number: 5
  // Column Number: 26

  // CallSite 2:
  // Function Name: anotherFunction
  // Script Name: /home/example.js
  // Line Number: 22
  // Column Number: 3

  // ...
}

// A function to simulate another stack layer
function anotherFunction() {
  exampleFunction();
}

anotherFunction();

import util from 'node:util';

interface Foo {
  foo: string;
}

const callSites = util.getCallSites({ sourceMap: true });

// With sourceMap:
// Function Name: ''
// Script Name: example.js
// Line Number: 7
// Column Number: 26

// Without sourceMap:
// Function Name: ''
// Script Name: example.js
// Line Number: 2
// Column Number: 26

fs.access('file/that/does/not/exist', (err) => {
  const errorMap = util.getSystemErrorMap();
  const name = errorMap.get(err.errno);
  console.error(name);  // ENOENT
});

fs.access('file/that/does/not/exist', (err) => {
  const name = util.getSystemErrorMessage(err.errno);
  console.error(name);  // no such file or directory
});

fs.access('file/that/does/not/exist', (err) => {
  const name = util.getSystemErrorName(err.errno);
  console.error(name);  // ENOENT
});

import util from 'node:util';
import EventEmitter from 'node:events';

function MyStream() {
  EventEmitter.call(this);
}

util.inherits(MyStream, EventEmitter);

MyStream.prototype.write = function(data) {
  this.emit('data', data);
};

const stream = new MyStream();

console.log(stream instanceof EventEmitter); // true
console.log(MyStream.super_ === EventEmitter); // true

stream.on('data', (data) => {
  console.log(`Received data: "${data}"`);
});
stream.write('It works!'); // Received data: "It works!"

import EventEmitter from 'node:events';

class MyStream extends EventEmitter {
  write(data) {
    this.emit('data', data);
  }
}

const stream = new MyStream();

stream.on('data', (data) => {
  console.log(`Received data: "${data}"`);
});
stream.write('With ES6');

class Foo {
  get [Symbol.toStringTag]() {
    return 'bar';
  }
}

class Bar {}

const baz = Object.create(null, { [Symbol.toStringTag]: { value: 'foo' } });

util.inspect(new Foo()); // 'Foo [bar] {}'
util.inspect(new Bar()); // 'Bar {}'
util.inspect(baz);       // '[foo] {}'

import { inspect } from 'node:util';

const obj = {};
obj.a = [obj];
obj.b = {};
obj.b.inner = obj.b;
obj.b.obj = obj;

console.log(inspect(obj));
// <ref *1> {
//   a: [ [Circular *1] ],
//   b: <ref *2> { inner: [Circular *2], obj: [Circular *1] }
// }

import util from 'node:util';

console.log(util.inspect(util, { showHidden: true, depth: null }));

import util from 'node:util';

const o = {
  a: [1, 2, [[
    'Lorem ipsum dolor sit amet,\nconsectetur adipiscing elit, sed do ' +
      'eiusmod \ntempor incididunt ut labore et dolore magna aliqua.',
    'test',
    'foo']], 4],
  b: new Map([['za', 1], ['zb', 'test']]),
};
console.log(util.inspect(o, { compact: true, depth: 5, breakLength: 80 }));

// { a:
//   [ 1,
//     2,
//     [ [ 'Lorem ipsum dolor sit amet,\nconsectetur [...]', // A long line
//           'test',
//           'foo' ] ],
//     4 ],
//   b: Map(2) { 'za' => 1, 'zb' => 'test' } }

// Setting `compact` to false or an integer creates more reader friendly output.
console.log(util.inspect(o, { compact: false, depth: 5, breakLength: 80 }));

// {
//   a: [
//     1,
//     2,
//     [
//       [
//         'Lorem ipsum dolor sit amet,\n' +
//           'consectetur adipiscing elit, sed do eiusmod \n' +
//           'tempor incididunt ut labore et dolore magna aliqua.',
//         'test',
//         'foo'
//       ]
//     ],
//     4
//   ],
//   b: Map(2) {
//     'za' => 1,
//     'zb' => 'test'
//   }
// }

// Setting `breakLength` to e.g. 150 will print the "Lorem ipsum" text in a
// single line.

import { inspect } from 'node:util';

const obj = { a: 1 };
const obj2 = { b: 2 };
const weakSet = new WeakSet([obj, obj2]);

console.log(inspect(weakSet, { showHidden: true }));
// WeakSet { { a: 1 }, { b: 2 } }

import { inspect } from 'node:util';
import assert from 'node:assert';

const o1 = {
  b: [2, 3, 1],
  a: '`a` comes before `b`',
  c: new Set([2, 3, 1]),
};
console.log(inspect(o1, { sorted: true }));
// { a: '`a` comes before `b`', b: [ 2, 3, 1 ], c: Set(3) { 1, 2, 3 } }
console.log(inspect(o1, { sorted: (a, b) => b.localeCompare(a) }));
// { c: Set(3) { 3, 2, 1 }, b: [ 2, 3, 1 ], a: '`a` comes before `b`' }

const o2 = {
  c: new Set([2, 1, 3]),
  a: '`a` comes before `b`',
  b: [2, 3, 1],
};
assert.strict.equal(
  inspect(o1, { sorted: true }),
  inspect(o2, { sorted: true }),
);

import { inspect } from 'node:util';

const thousand = 1_000;
const million = 1_000_000;
const bigNumber = 123_456_789n;
const bigDecimal = 1_234.123_45;

console.log(inspect(thousand, { numericSeparator: true }));
// 1_000
console.log(inspect(million, { numericSeparator: true }));
// 1_000_000
console.log(inspect(bigNumber, { numericSeparator: true }));
// 123_456_789n
console.log(inspect(bigDecimal, { numericSeparator: true }));
// 1_234.123_45

import { parseArgs } from 'node:util';
const args = ['-f', '--bar', 'b'];
const options = {
  foo: {
    type: 'boolean',
    short: 'f',
  },
  bar: {
    type: 'string',
  },
};
const {
  values,
  positionals,
} = parseArgs({ args, options });
console.log(values, positionals);
// Prints: [Object: null prototype] { foo: true, bar: 'b' } []

import { parseEnv } from 'node:util';

parseEnv('HELLO=world\nHELLO=oh my\n');
// Returns: { HELLO: 'oh my' }

import util from 'node:util';
import fs from 'node:fs';

const stat = util.promisify(fs.stat);
stat('.').then((stats) => {
  // Do something with `stats`
}).catch((error) => {
  // Handle the error.
});

import util from 'node:util';
import fs from 'node:fs';

const stat = util.promisify(fs.stat);

async function callStat() {
  const stats = await stat('.');
  console.log(`This directory is owned by ${stats.uid}`);
}

callStat();