How to Create Function in JavaScript: Syntax and Examples

In JavaScript, you create a function using the function keyword followed by a name, parentheses (), and curly braces {} containing the code to run. You can also create functions using arrow syntax with () => {} for shorter code.

Syntax

A JavaScript function is created using the function keyword, followed by the function name, parentheses () for parameters, and curly braces {} enclosing the code block. Parameters are optional and allow you to pass values into the function.

Example parts:

• function: keyword to declare a function
• name: the function's identifier
• parameters: inputs inside parentheses, separated by commas
• body: code inside curly braces that runs when the function is called

javascript

function greet(name) {
  console.log('Hello, ' + name + '!');
}

Example

This example shows a function named greet that takes a name parameter and prints a greeting message. It demonstrates how to define and call a function.

javascript

function greet(name) {
  console.log(`Hello, ${name}!`);
}

greet('Alice');

Output

Hello, Alice!

Common Pitfalls

Common mistakes include forgetting parentheses when calling a function, missing curly braces, or not passing required parameters. Another pitfall is confusing function declaration with function expression or arrow functions.

Also, avoid naming functions with reserved words or starting names with numbers.

javascript

/* Wrong: missing parentheses when calling */
function sayHi() {
  console.log('Hi!');
}
sayHi; // Does nothing

/* Right: call with parentheses */
sayHi();

Output

Hi!

Quick Reference

Syntax	Description
function name(params) { code }	Declare a named function
const name = function(params) { code }	Function expression assigned to a variable
const name = (params) => { code }	Arrow function syntax
name()	Call a function

Key Takeaways

Use the function keyword followed by name and parentheses to create a function.

Call functions with parentheses to run their code.

Parameters let you pass data into functions.

Arrow functions provide a shorter syntax for creating functions.

Avoid common mistakes like missing parentheses or curly braces.