17 JavaScript One-Liners

const hasFocus = (ele) => ele === document.activeElement;

const siblings = (ele) => [].slice.call(ele.parentNode.children).filter((child) => child !== ele);

// or const siblings = (ele) => [...ele.parentNode.children].filter((child) => child !== ele);

const getSelectedText = () => window.getSelection().toString();

history.back();
// or history.go(-1);

const clearCookies = () => document.cookie
  .split(';')
  .forEach((c) =>(document.cookie = c.replace(/^ +/, '')
  .replace(/=.*/, `=;expires=${new Date().toUTCString()};path=/`)));

// `a` and `b` are an array const isEqual = (a, b) => JSON.stringify(a) === JSON.stringify(b);
// or const isEqual = (a, b) => a.length === b.length && a.every((v, i) => v === b[i]);

// Example isEqual([1, 2, 3], [1, 2, 3]); // true
isEqual([1, 2, 3], [1, '2', 3]); // false

const toObject = (arr, key) => arr.reduce((a, b) => ({ ...a, [b[key]]: b }), {});
// or const toObject = (arr, key) => Object.fromEntries(arr.map((it) => [it[key], it]));

// Example toObject([
  { id: '1', name: 'Alpha', gender: 'Male' },
  { id: '2', name: 'Bravo', gender: 'Male' },
  { id: '3', name: 'Charlie', gender: 'Female' }],
'id');

/*
{
'1': { id: '1', name: 'Alpha', gender: 'Male' },
'2': { id: '2', name: 'Bravo', gender: 'Male' },
'3': { id: '3', name: 'Charlie', gender: 'Female' }
}
*/

const countBy = (arr, prop) => arr.reduce((prev, curr) => ((prev[curr[prop]] = ++prev[curr[prop]] || 1), prev), {});

// Example countBy([
{ branch: 'audi', model: 'q8', year: '2019' },
{ branch: 'audi', model: 'rs7', year: '2020' },
{ branch: 'ford', model: 'mustang', year: '2019' },
{ branch: 'ford', model: 'explorer', year: '2020' },
{ branch: 'bmw', model: 'x7', year: '2020' },
],
'branch');

// { 'audi': 2, 'ford': 2, 'bmw': 1 }

const isNotEmpty = (arr) => Array.isArray(arr) && Object.keys(arr).length > 0;

// Example isNotEmpty([]); // false
isNotEmpty([1, 2, 3]); // true

const isEqual = (...objects) => objects.every((obj) => JSON.stringify(obj) === JSON.stringify(objects[0]));

// Example isEqual({ foo: 'bar' }, { foo: 'bar' }); // true
isEqual({ foo: 'bar' }, { bar: 'foo' }); // false

const pluck = (objs, property) => objs.map((obj) => obj[property]);

// Example pluck([
  { name: 'John', age: 20 },
  { name: 'Smith', age: 25 },
  { name: 'Peter', age: 30 },
],
'name');

// ['John', 'Smith', 'Peter']

const invert = (obj) => Object.keys(obj).reduce((res, k) => Object.assign(res, { [obj[k]]: k }), {});
// or const invert = (obj) => Object.fromEntries(Object.entries(obj).map(([k, v]) => [v, k]));

// Example invert({ a: '1', b: '2', c: '3' }); // { 1: 'a', 2: 'b', 3: 'c' }

const removeNullUndefined = (obj) =>
  Object.entries(obj).reduce(
    (a, [k, v]) => (v == null ? a : ((a[k] = v), a)),
    {},
  );

// or const removeNullUndefined = (obj) =>
  Object.entries(obj)
    .filter(([_, v]) => v != null)
    .reduce((acc, [k, v]) => ({ ...acc, [k]: v }), {});

// or const removeNullUndefined = (obj) =>
  Object.fromEntries(Object.entries(obj).filter(([_, v]) => v != null));

// ExampleremoveNullUndefined({
  foo: null,
  bar: undefined,
  fuzz: 42
});
// { fuzz: 42 }

const sort = (obj) =>
  Object.keys(obj)
    .sort()
    .reduce((p, c) => ((p[c] = obj[c]), p), {});

// Example const colors = {
  white: '#ffffff',
  black: '#000000',
  red: '#ff0000',
  green: '#008000',
  blue: '#0000ff',
};
sort(colors);
/*
{
  black: '#000000',
  blue: '#0000ff',
  green: '#008000',
  red: '#ff0000',
  white: '#ffffff',
}
*/

const isPromise = (obj) =>
  !!obj &&
  (typeof obj === 'object' || typeof obj === 'function') &&
  typeof obj.then === 'function';

const isArray = (obj) => Array.isArray(obj);