17 JavaScript One-Liners

1. DOM & BOM related

1. Check if the element has focus
2. Get all sibling nodes of an element
3. Get the selected text
4. Return to the previous page
5. Clear all cookies
6. Convert cookies to objects

2. Array related

7. Comparing two arrays
8. Convert an array of objects to an object
9. Counting by properties of an array of objects
10. Check if the array is empty

3. Object Related

11. Check if multiple objects are equal
12. Extracting attribute values from an array of objects
13. Reverse the keys and values of an object
14. Remove all empty and undefined properties from objects
15. Sort objects by properties
16. Check if an object is a Promise
17. Check if the object is an array

1. DOM & BOM related

1. Check if the element has focus

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

2. Get all sibling nodes of an element

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

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

3. Get the selected text

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

4. Return to the previous page

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

5. Clear all cookies

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

6. Convert cookies to objects

const cookies = document.cookie
.split(';')
.map((item) => item.split('='))
.reduce((acc, [k, v]) => (acc[k.trim().replace('"', '')] = v) && acc, {});

2. Array related

7. Comparing two arrays

// `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

8. Convert an array of objects to an object

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' }
}
*/

9. Counting by properties of an array of objects

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 }

10. Check if the array is empty

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

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

3. Object Related

11. Check if multiple objects are equal

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

12. Extracting attribute values from an array of objects

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']

13. Reverse the keys and values of an object

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' }

14. Remove all empty and undefined properties from objects

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 }

15. Sort objects by properties

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',
}
*/

16. Check if an object is a Promise

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

17. Check if the object is an array

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

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