Single line of code! No more!

Check if an array is empty

// arr is an array
const isEmpty = arr => !Array.isArray(arr) || arr.length === 0;

// Examples
isEmpty([]); // true
isEmpty([1, 2, 3]); // false

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Clone an array
-------------------------------.

// arr is an array
const clone = arr => arr.slice(0);

// Or
const clone = arr => [...arr];

// Or
const clone = arr => Array.from(arr);

// Or
const clone = arr => arr.map(x => x);

// Or
const clone = arr => JSON.parse(JSON.stringify(arr));

// Or
const clone = arr => arr.concat([]);

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Compare two arrays regardless of order

// a and b are arrays
const isEqual = (a, b) => JSON.stringify(a.sort()) === JSON.stringify(b.sort());

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

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Compare two arrays
// a and b are arrays
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]);

// Examples
isEqual([1, 2, 3], [1, 2, 3]); // true

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

Convert an array of objects to a single object

const toObject = (arr, key) => arr.reduce((a, b) => ({ ...a, [b[key]]: b }), {});

// 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' },
}

*/

Convert an array of strings to numbers
const toNumbers = arr => arr.map(Number);

// Or
const toNumbers = arr => arr.map(x => +x);

// Example

toNumbers(['2', '3', '4']); // [2, 3, 4]

Count by the 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 }

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Count the occurrences of a value in an array

const countOccurrences = (arr, val) => arr.reduce((a, v) => (v === val ? a + 1 : a), 0);

// Examples
countOccurrences([2, 1, 3, 3, 2, 3], 2); // 2
countOccurrences(['a', 'b', 'a', 'c', 'a', 'b'], 'a'); // 3

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