What is the difference between function declaration and function expression?

Function Declaration — is a function statement with a name that is hoisted into the scope. Such functions can be called before their definition in the code.

function greet() {
  console.log('Hello');
}
greet(); // works

Function Expression — is an assignment of a function (anonymous or named) to a variable. These functions are not hoisted, and can only be called after their definition.

const greet = function() {
  console.log('Hello');
};
greet(); // works

The difference is that function declaration creates a function at compile time, while function expression does so at runtime, affecting the order of calls and scope.