Arrow Functions

Mission: Backstage Toolkit

A backstage calculation can be written as an arrow function instead of a function declaration. Try three short calculations in script.js and check their results in the Console.

An arrow function is another way to store a function in a variable. For a single expression, the expression's value is returned automatically. You will meet function expressions and callbacks in more detail later; for now, compare this with the function declaration you just used.

Syntax variations

// Function declaration from the previous lesson
function traditionalAdd(a, b) { return a + b; }

// Arrow function — same result, stored in a variable
const add = (a, b) => a + b;

// Single parameter — parentheses optional
const double = n => n * 2;

// No parameters — empty parentheses required
const greet = () => "Hello!";

// Multi-line body — needs {} and explicit return
const classify = n => {
    if (n > 0) return "positive";
    if (n < 0) return "negative";
    return "zero";
};
console.log(add(2, 3), double(4)); // 5 8

For this exercise, use an arrow function for each calculation. Arrow functions also differ in how they handle this and constructors; those details matter later when you learn objects and classes.

For temperature conversion, Math.round(value * 10) / 10 rounds to one decimal place: scaling by ten makes the first decimal a whole number before rounding. You will explore Math in the built-ins module.