Ahmed Abdulrahman's Desk

Check if all values in an array are equal

You can check it using every method on the array:

1const areEqual = arr => {
2  return arr.length > 0 && arr.every(item => item === arr[0]);
3}
4// areEqual([11, 32, 21, 54]) === false 🚫
5// areEqual(['blue', 'blue', 'blue']) === true ✅

Convert an array of strings value to numbers

JS provides different ways to convert a string value into a number, but the best one is to use Number object in a non-constructor context (without the new keyword). It also takes care of the decimals as well:

1const toNumbers = arr => arr.map(Number);
2// toNumbers(["2", "3", "4"]) returns [2, 3, 4]

Create an array of cumulative sum

To get the summation of a sequence of numbers in an array, we can use currying to access the previous value:

1const accumulate = arr => {
2  return arr.map((sum => value => sum += value)(0));
3}
4
5/*
6accumulate([1, 2, 3, 4]) === [1, 3, 6, 10]
7// 1             = 1
8// 1 + 2         = 3
9// 1 + 2 + 3     = 6
10// 1 + 2 + 3 + 4 = 10
11*/

Create an array of numbers in the given range

To create an array that contains all numbers between starting index and ending index, including starting index and ending index themselves:

1const range = (min, max) => {
2  return Array(max - min + 1).fill(0).map((_, i) => max - min + i)
3};
4// range(5, 10) === [5, 6, 7, 8, 9, 10]

Empty an array

JS provides various ways of clearing existing array:

1const empty = arr => arr.length = 0;
2
3// Or using splice but since the .splice() function will return an array
4// with all the removed items, it will actually return a copy of
5// the original array
6const empty = arr => arr.splice(0, arr.length)
7
8// Or
9arr = [];

Find the maximum or minimum item of an array

1const max = arr => Math.max(...arr);
2const min = arr => Math.min(...arr);

Check if an object is an array

1const isArray = obj => Array.isArray(obj);

Get a random item from an array

1const randomItem = arr => {
2  return arr[Math.floor(Math.random() * arr.length)]
3};

Get the average of an array

1const average = arr => {
2  return arr.reduce((a, b) => a + b, 0) / arr.length;
3}

Get the sum of array of numbers

1const sum = arr => arr.reduce((a, b) => a + b, 0);

Get the unique values of an array

1const unique = arr => [...new Set(arr)];
2
3// Or
4const unique = arr => {
5  return arr.filter((el, i, array) => array.indexOf(el) === i);
6}

Merge two arrays

We can achieve this in different ways:

1// 1 - To just merge the arrays (without removing duplicates)
2const merge = (a, b) => a.concat(b);
3// OR
4const merge = (a, b) => [...a, ...b];
5
6// 2 -  To merge the arrays and removing duplicates
7const merge = [...new Set(a.concat(b))];
8// OR
9const merge = [...new Set([...a, ...b])];