# Function Declaration vs Function Expression: What’s the Difference? Imagine you need to do a certain task again and again. And you writing the same piece of code more than one time just to do the same task. That will a a very in-efficient way to write code. You can use functions, let’s understand it > ## What Functions are Functions includes a **block of code**, which will **run once we call them**. It is **reusable**. So we can call the function as many times as we want. Now we won’t have to write the same code again and again. ```javascript function add(a,b){ return a+b } add(2,3) // 5 add(3,4) // 7 ``` ### Why we need Functions Functions are extremely important in programming because they help organize and reuse code. * **Code Reusability -** You can write code **once** and use it many times. * **Cleaner and Organized Code** - The code becomes **shorter and easier to read**. * **Programs Easier to Maintain -** If you need to change logic, you only update it **in one place**. * **Helps Break Big Problems into Small Parts -** Large applications are built using many small functions. > ## Function Declaration Syntax A function declaration is the most common way to create a function in JavaScript. Here the function is created using ‘function’ keyword and we can accept parameters. Can be **called before it is defined** because of **hoisting .** ```javascript sayHello(); // Hello function sayHello() { console.log("Hello"); } // This works because function declarations are hoisted. ``` > ## Function Expression Syntax A function expression is when the function is stored inside a variable. These are nameless function. And function keyword is optional, you can also use arrow function over there. ```javascript // Syntax const variableName = function(parameters) { // code to execute }; // Example const greet = function(name) { console.log("Hello " + name); }; greet("Mehtab"); // Hello Mehtab ``` Example (this will cause an error): ```javascript greet("Mehtab"); // error -> Because the variable is not initialized yet const greet = function(name) { console.log("Hello " + name); }; ``` **Quick Comparison**

Feature	Function Declaration	Function Expression
Syntax	function greet(){}	const greet = function(){}
Hoisting	Yes	No
Function name	Required	Optional
Stored in variable	No	Yes

![](https://cdn.hashnode.com/uploads/covers/69078637d192b5f0327809a3/9ecc534a-30e5-45c0-a2bb-0d4a3ce833f3.png align="center") > ## When to use each type ### **When to Use Function Declaration** Use **function declarations** when the function is a **main part of your program** and should be available everywhere in the file. **Good for:** * Utility functions * Functions used multiple times * Functions you want to call before they appear in the code ### When to use Function Expression Use **function expressions** when you want to **store a function inside a variable** or **pass it around like data**. **Good for:** * Callback functions * Functions inside other functions * Functions used once * More controlled execution ## Conclusion This concludes our blog, where we understood function structure and two types function declaration and function expression. And when to use each type. * * *