Originally published on php-to-js.learnio.dev — part of the PHP to JavaScript course. View this lesson on the original site.

Three ways to define a function — pick by hoisting and `this`

PHP named functions, anonymous closures, and PHP 7.4 arrow functions map cleanly to JavaScript declarations, expressions, and arrows.

PHP habit

<?php
function greet(string $name): string {
    return "Hello, $name";
}

$multiply = function (int $a, int $b): int {
    return $a * $b;
};

$double = fn(int $n) => $n * 2;

JavaScript equivalent

function greet(name) {
  return `Hello, ${name}`;
}

const multiply = function (a, b) {
  return a * b;
};

const double = (n) => n * 2;

Form	Hoisted?	Typical use
`function name() {}`	Yes	Top-level helpers, utilities
`const fn = function() {}`	No	Assign to variable, pass as value
`const fn = () => {}`	No	Callbacks, short transforms

Hoisting in practice

console.log(add(2, 3)); // 5 — declaration exists before its line

function add(a, b) {
  return a + b;
}

// console.log(multiply(2, 3)); // ReferenceError
const multiply = (a, b) => a * b;

Declarations behave like PHP functions defined in a file before use. Expressions and arrows follow const rules — define before call.

Arrow bodies: expression vs block

const square = (n) => n * n;

const clamp = (value, min, max) => {
  if (value < min) return min;
  if (value > max) return max;
  return value;
};

One expression after => returns automatically. Use { } when you need multiple statements.

`this` preview — arrows inherit, functions bind

Arrow functions do not get their own this. Regular functions do. That matters for object methods and DOM handlers later; for now, default to arrows in callbacks and declarations for named top-level functions.

Try it

Use the amber Try it panel below. Click Run.

function formatPrice(amount, currency = 'GBP') {
  return new Intl.NumberFormat('en-GB', { style: 'currency', currency }).format(amount);
}

const applyDiscount = (price, percent) => price * (1 - percent / 100);

console.log(formatPrice(49.99));
console.log(applyDiscount(100, 10));

Same layering you use in PHP: a named function for a clear entry point, a short closure for a one-off transform.

From PHP to JavaScript — JavaScript Syntax Foundations for PHP Devs

Three ways to define a function — pick by hoisting and this