How To Define a JavaScript Function

There are a few different ways to declare a function in Javascript applications. I’ve laid out 4 ways below so choose the method that best fits your use case! Function declarations are great for named functions, whereas arrow functions are excellent for callbacks and shorter functions.  

Using Function Declaration

 /** Function Declaration */

 function functionName(parameters) {

    // code to be executed

    return value;

 }

 // Example

 function greet(name) {

    return "Hello, " + name + "!";

 }

 console.log(`My name is ${greet("Alice")}`); // "Hello, Alice!"

Using Function Expression

 /** Function Expression */

 const functionName = function(parameters) {

    // code to be executed

    return value;

 };

 // Example

 const multiply = function(a, b) {

    return a * b;

 };

 console.log(`5 * 3 = ${multiply(5, 3)}`); // 15

Using Arrow Functions (ES6)

 /** Arrow Function (ES6) */

 const functionName = (parameters) => {

    // code to be executed

    return value;

 };

 // Examples with different syntax

 const square = (x) => {

    return x * x;

 };

 console.log(`Square of 4: ${square(4)}`); // 16

 // Implicit return (for single expressions)

 const squareRoot = x => x ** 0.5;

 console.log(`Square Root of 8: ${squareRoot(8)}`);

 // Multiple parameters

 const add = (a, b) => a + b;

 console.log(`2 + 3 = ${add(2, 3)}`); // 5

 // No parameters

 const title = () => "Math";

 console.log(`The page title is "${pageTitle()}"`);

Using the Function Constructor

 /** 4. Function Constructor (less common) */

 const functionName = new Function("parameters", "function body");

 // Example

 const divide = new Function("a", "b", "return a / b;");

 console.log(divide(10, 2)); // 5