JS has 4 kinds of functions:

• Regular function: can return anything; always runs to completion after invocation.
• Generator function: returns a Generator object; can be paused and resumed with the yield operator
• Async function: returns a Promise; can be paused and resumed with the await operator
• Async generator function: returns an AsyncGenerator object; both the await and yield operators can be used

Classes are conceptually not functions (because they throw an error when called without new), but they also inherit from Function.prototype and have typeof MyClass === "function".

// Constructor
const multiply = new Function("x", "y", "return x * y");

// Declaration
function multiply(x, y) {
    return x * y;
}

// Expression; the function is anonymous but assigned to a variable
const multiply = function (x, y) {
    return x * y;
};

// Expression; the function has its own name
const multiply = function funcName(x, y) {
    return x * y;
};
                    
// Arrow function
const multiply = (x, y) => x * y;
                    
// Method
const obj = {
    multiply(x, y) {
        return x * y;
    },
};