1.5 Predefined Objects in JavaScript

There are lots of built-in objects in JavaScript. You've used some of them, such as arrays:

let arr = [1, 2, 4, 8, 16];
console.log(arr);

and functions (yes, they are objects):

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

Common Objects

Here are some common objects worth introducing:

Wrapper Objects

Wrapper object types (Number, String, Boolean) serve as object "versions" of their corresponding primitive type.

We can declare and initialize them as we would declare any other object type:

let firstName = new String("Mark"), lastName = new String("Smith");

// same as

let firstName = "Mark", lastName = "Smith";

Wrapper objects can be used in a similar fashion to their corresponding primitive type (i.e. concatenation on String objects):

let firstName = new String("Mark"), lastName = new String("Smith");
let name = new String("");
name = firstName + " " + lastName;
console.log(name, ": Hi!");

However, like many other objects, wrapper objects are far more useful and complex under the hood.