Data types

In programming, we have the concept of a data type. When we think about things in our head like sentences and numbers, we imagine them in fundamentally different ways. For example, a sentence can't be multiplied by 100, and a number can't be made up of different words.

In programming, we also have this distinction between different things. There are many data types, but here we'll look at the most fundamental.

Numbers

Numbers are, well, numbers. They can be added to, subtracted from, multiplied, and divided. If I have a program that runs 1 + 2, it will give me 3. In JavaScript, numbers are written as numbers — 1 is a number, and so is 57.87, and even -95.01, but there are some important rules for how numbers work (in JavaScript). One important thing to keep in mind is that numbers can’t contain commas, so 1,000,000 isn't a valid number (however, you can use _, so 1_000_000 is the same as 1000000). Finally, number literals (a literal is a number written in our code, so 10 is a literal, while (10) and a (where a is const a = 9;) aren’t) can’t have functions ran directly on them. We'll get into this more later, but keep in mind that 10.toString() is not valid, while (10).toString() is.

Strings

Strings are essentially text. They're made up of anything and can hold any number of characters (letters, numbers, or symbols). In fact, this document is being stored as a string.

Strings are defined using either a ", ', or `. For example, I can write a string as "Hello world!", 'Hello world!', or `Hello world!`. As a rule of thumb, don't include the enclosing character (", ', or `) inside of the string itself (so 'Don't do this' is invalid). We'll get into ways to get around this in a bit, though.

Booleans

Booleans essentially store yes or no values. You can create a boolean using either true (yes) or false (no). Right now, booleans won't be all that useful, but later on they'll become extremely important.

Conversions

In many cases, we'll need to convert between the data types listed above. For example, if I have some user input, it'll be a string because the user can type any text value on their keyboard. However, if I want it to be a number (maybe I want to divide it by 20), I'll need to convert it from a string to a number.

Anything -> String

Almost anything can be converted to a string using the toString() method. For example, if I wanted to convert 42 to a string, I could use (42).toString() (note that 42 is in parentheses because certain types, including numbers, need parentheses around them to have methods called on them).

String -> Number

To convert a string to a number, we can use the Number() method, for example with Number("101"). Check out the code example to see the difference more highlighted.