What is the difference between function declarations and function expressions?

A function declaration defines a named function using the function keyword.
It is hoisted completely, meaning you can call the function before it is defined in the code.

✅ Example:

sayHello(); // ✅ Works due to hoisting

function sayHello() {
  console.log("Hello from declaration!");
}

sayHello(); // ✅ Works due to hoisting

function sayHello() {
  console.log("Hello from declaration!");
}

A function expression assigns a function (anonymous or named) to a variable.
Only the variable declaration is hoisted, not the function definition.
That means you cannot call it before defining it.

✅ Example:

sayHi(); // ❌ Error: Cannot access 'sayHi' before initialization

const sayHi = function () {
  console.log("Hello from expression!");
};

sayHi(); // ❌ Error: Cannot access 'sayHi' before initialization

const sayHi = function () {
  console.log("Hello from expression!");
};

Feature	Function Declaration	Function Expression
Hoisting	Fully hoisted (can be called before definition)	Only variable is hoisted (function not available before definition)
Syntax	`function name() {}`	`const name = function() {}`
Use case	When you want functions available throughout scope	When you want functions conditionally, inline, or assigned
Anonymous functions	Not possible (always needs a name)	Possible (can be anonymous or named)

👉 In short:

Declarations → Hoisted, global availability.
Expressions → Not hoisted (only the variable is), often used in callbacks or assigned to variables.

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