Function expressions

JavaScript course · Beginner · Lesson 51/133

Learn the anonymous function expression assigned to a variable.

Function expressions

In JavaScript, functions are values, so you can assign them to a variable. This is called a function expression. The definition starts with the function keyword but does not need a name.

Example: const add = function(a, b) { return a + b; };. Here the unnamed function is assigned to add. It is also called an anonymous function. You call it the same way: add(3, 5).

const for functions

Using const in a function expression is a common choice; it prevents reassignment. Example: const greet = function(name) { console.log("Hi " + name); };.

Here greet is a constant variable, but the function inside can still be called: greet("Alex"). You can also use let, but const is safer because it blocks accidental reassignment.

Exercise Constant function expression

Assign a function expression to a variable called square. The function should take an n parameter and return n * n. Then print the result with console.log(square(6)).

Show example solution

const square = function(n) {
  return n * n;
};

console.log(square(6));

Test yourself

Which of these is a function expression?
- function greet() { }
- greet() { }
- const greet = ();
- const greet = function() { };
Show answer

const greet = function() { }; — Correct. Assigning a function to a variable is a function expression.

Complete the function expression

const multiply = ____(a, b) {
  return a * b;
};
console.log(multiply(3, 4));

Show answer

const multiply = function(a, b) {
  return a * b;
};
console.log(multiply(3, 4));

Match each form to its name

function greet() { }

Function declaration
const greet = function() { };

Function expression
greet()

Function call
function() { }

Anonymous function

All lessons in Beginner

1 Variables and data types

Function expressions