Function Expression

In JavaScript, a function expression is a way to define a function as part of an expression. Unlike function declarations, function expressions are not hoisted, which means they cannot be called before they are defined in the code.

Here's the basic syntax of a function expression:

let functionName = function(parameters) {
	// Code to be executed
	// ...
	return value; // Optional return statement
};

The function keyword is followed by an optional name for the function. If a name is provided, it becomes a named function expression; otherwise, it's an anonymous function expression. The parameters are specified in parentheses, and the function body is enclosed in curly braces.

Here's an example of a named function expression:

let add = function sum(a, b) {
	return a + b;
};

console.log(add(3, 5)); // Output: 8

In this example, add is the variable that holds the function, and sum is the optional name of the function. Even though the function has a name, you cannot call sum directly; you must use the variable add.

Here's an example of an anonymous function expression:

let multiply = function(a, b) {
	return a * b;
};

console.log(multiply(4, 2)); // Output: 8

In this case, the function does not have a name, and it's directly assigned to the variable multiply.

Function expressions are often used when you want to pass a function as an argument to another function, or when you want to create a function on the fly.