PHP variable declaration

$variable = 1;

JS alternative

let variable = 1;

PHP - check if the variable exists

if (isset($variable))

JS alternative

if (typeof variable !== "undefined")

PHP count array elements

$count = count([2, 3, 4]);

JS alternative

let count = [2, 3, 4].length;

PHP count letters in the string

$len = strlen('some string');

JS alternative

let len = 'some string'.length;

PHP absolute value of a given number

$variable = abs(-5);

JS alternative

let variable = Math.abs(-5);

PHP - power of a number

$square = pow(5, 2);

JS alternative

let square = Math.pow(5, 2);

PHP - square root of a number

$square_root = sqrt(16);

JS alternative

let square_root = Math.sqrt(16);

PHP - minimum number

$max = min(2, 3, 4);

JS alternative

let max = Math.min(2, 3, 4);

PHP - maximum number

$max = max([2, 3, 4]);

JS alternative

let max Math.max(...[2, 3, 4])

PHP calculates sum of the array elements

$sum = array_sum([2, 3, 4]);

JS alternative

let sum = 0;
let arr = [1, 2, 3];
for (let value of arr) {
    sum += value;
}

Another way to calculate the same

let arr = [1, 2, 3];
let sum = 0;
let len = arr.length;
for (let i = 0; i < len; sum += arr[i++]);

PHP - string position

$pos = strpos('Hello world', 'world');

JS alternative

let pos = 'Hello world'.indexOf('world');

PHP - edit letter in a string

$string[4] = 'X';

JS alternative

string = string.substring(0, 4) + 'X' + string.substring(5);

PHP convert the variable to integer

$variable = intval(5.5);

JS alternative

let variable = parseInt(5.5);

PHP - explode the sentence

$sentence = "Lorem ipsum dolor st amet";
$words = explode(" ", $sentence);

JS alternative

let sentence = "Lorem ipsum dolor st amet";
let words = sentence.split(" ");