In JavaScript, functions are more than just simple procedures; they are actually objects. Let’s explore how this fundamental aspect of JavaScript affects how functions are used and understood.
When you use the typeof operator on a function, you’ll find something interesting:
function add(x, y) {
return x + y;
}
console.log(typeof add); // Outputs "function"Although typeof returns “function”, it’s important to understand that functions in JavaScript are a special type of object—Function objects, to be precise. This is why functions can do everything that other objects can do, such as being stored in variables, passed as arguments, and more. (We will cover these in the next chapter.)
Just like other objects in JavaScript, functions can be dynamically created using the Function constructor. This method takes strings as arguments, specifying parameters and the function body:
const multiply = new Function("x", "y", "return x * y;");
console.log(typeof multiply); // Outputs "function"
console.log(multiply(2, 3)); // Outputs 6While using the Function constructor can be useful in some dynamic programming scenarios, it’s generally less efficient and harder to read than declaring functions directly.
Since functions are objects, they come with built-in properties and methods. For instance:
function add(x, y) {
return x + y;
}
console.log(add.name); // Outputs "add"
console.log(add.length); // Outputs 2, the number of parameters
console.log(add.toString()); // Outputs the function's code as a stringname: Returns the name of the function.length: Returns the number of formal parameters the function accepts.toString(): Returns a string representing the function’s source code.These properties can be incredibly useful for debugging purposes or for dynamic function handling in applications that manipulate functions as first-class citizens.