JavaScript's Built in Objects and Classes Built in Objects

Learning objective: By the end of this lesson, learners will be able to use and explain JavaScript’s Math object, applying methods such as .random() and .floor(), and create functions for generating random integers.

Built-In Objects

The Math. object in JavaScript is very useful for different tasks that require mathematics. For example, when you need random numbers for things like making unique IDs or shuffling items in a list.

Math has many special functions. One important one is .random(). This function gives you a random number between 0 (including 0) and 1 (but not reaching 1):

Math.random() // you might get a result like: 0.5570349614485068

Math also has functions that change numbers in specific ways. For example, .floor() makes a number smaller to the nearest whole number:

let num = 1.21
Math.floor(num) // gives you 1

This method has a return value of the largest integer less than or equal to the value of num. In other words, it removes or truncates everything after the decimal.

When combined, you can see how the built-in Math object can dramatically shorten code and make life easier. Without having to code out either method, we can create a function that gets a random integer from a maximum value:

function getRandomInt(max) {
  return Math.floor(Math.random() * max);
}

In addition to methods, the JavaScript Math object also contains certain values, such as PI:

Math.PI // => 3.141592653589793

Now that we’ve taken a look at an example of a built-in Javascript object and refreshed ourselves on dot notation, let’s take a look at a built-in class.