Primitive Data Types
Updated on Dec 22, 2021 by Alan Morel
Table of Contents
Let's explore all of JavaScript's primitive data types. A data type describes what kind of data is being held, and the reason why the following data types are referred to as primitive is because they are considered basic building blocks of the programming language. JavaScript has a number of primitive data types, each one with its own unique properties and methods.
Number
Numbers are pretty self-explanatory. After you declare a variable, you can initialize it with a number of any kind, and it will retain that value.
const cars = 7;
console.log(cars);
7
Numbers are used extensively in JavaScript, as they are one of the most common data types.
String
Strings in JavaScript are text that you can assign to a variable. You can concatenate (combine) two strings by using the + operator. Under the hood, strings are just arrays of characters.
const city = "New York City";
console.log("The greatest city in the world is " + city + ".");
The greatest city in the world is New York City.
Template Literals
An alternate way to work with strings in JavaScript is template literals. Template literals are useful because they support multiple lines and string interpolation (being able to insert variables).
console.log(`Look how
cool this string is.
It is on multiple lines!`);
Look how
cool this string is.
It is on multiple lines!
Template literals allow you to avoid using the newline character or needing to escape anything.
String Interpolation
String interpolation lets you easily use variables inside your strings via its ${variable} syntax. Here's an example:
const restaurant = "Chipotle";
console.log(`My favorite restaurant is ${restaurant}!`);
My favorite restaurant is Chipotle!
String interpolation is useful for inserting variables into strings and is recommended over concatenation because it's easier to read and maintain.
ToLowerCase
Calling toLowerCase on a string will return the same string with any uppercased letters replaced with lowercase letters.
const place = "Mexico City";
console.log(place.toLowerCase());
mexico city
ToUpperCase
On the other hand, to do the reverse and capitalize all letters in a string, simply call toUpperCase on it. This will return the same string with all lowercase letters replaced with uppercase letters.
const place = "Mexico City";
console.log(place.toUpperCase());
MEXICO CITY
Repeat
You can repeat a string as many times as you want using the repeat method. It takes a number as the parameter representing how many times you'd like the string to repeat. Here's an example:
const phrase = " time and";
const sentence = "I dominate in Fortnite" + phrase.repeat(3) + " time again.";
console.log(sentence);
I dominate in Fortnite time and time and time and time again.
Replace
There will be times when you will want to replace a certain substring with another substring inside a string.
For example, let's say you want to replace the word red with blue:
const sentence = "The house is red.";
const newSentence = sentence.replace("red", "blue");
console.log(newSentence);
The house is blue.
Includes
The last JavaScript string method we'll take a look at is the includes method. This method checks to see if a substring exists inside another string, and returns true if it does or false if it does not. Here's an example:
const sentence = "The house is red.";
console.log(sentence.includes("house"));
console.log(sentence.includes("tiger"));
true
false
Boolean
A boolean is a data type that has only two values, true or false. True generally means "correct" or "yes" while false generally means "incorrect" or "no".
const pizzaIsGood = true;
const wholeFoodsIsCheap = false;
Symbols
Symbols are tokens that serve as unique IDs. Because each one is different, you can use this to your advantage.
For example, you can use them to give values to constants that you define. Let's say you run a company that makes shirts. You can use symbols to keep track of all the sizes you sell:
const SIZE_XSMALL = Symbol();
const SIZE_SMALL = Symbol();
const SIZE_MEDIUM = Symbol();
const SIZE_LARGE = Symbol();
const SIZE_XLARGE = Symbol();
In the real world, each size is distinct, and so will each value in these constants. Now with this, you can write elegant code like this:
function getShirtsLeftInSize(size) {
if (size === SIZE_XSMALL) {
return 4;
} else if (size === SIZE_SMALL) {
return 6;
} else if (size === SIZE_MEDIUM) {
return 3;
} else if (size === SIZE_LARGE) {
return 7;
} else if (size === SIZE_XLARGE) {
return 12;
}
}
const mySize = SIZE_SMALL;
console.log("There are " + getShirtsLeftInSize(mySize) + " shirts left in your size.");
There are 6 shirts left in your size.
Sure, you could do this without using symbols like this:
const SIZE_XSMALL = "XSMALL";
const SIZE_SMALL = "SMALL";
const SIZE_MEDIUM = "MEDIUM";
const SIZE_LARGE = "LARGE";
const SIZE_XLARGE = "XLARGE";
But the problem with that is that none of the values of these constants can be guaranteed to be unique. Nothing would stop anybody from just creating a new string variable and assigning it a valid size name:
const mySize = "SMALL";
That would still work, but it requires knowing the exact value of the constant, whereas with symbols, you just need the name of it. This is why symbols are so useful.
Null
Null is a special value in JavaScript that essentially means nothing. It's often used to indicate that a variable has no value.
const pears = null;
The variable pears is empty and void of a value.
Undefined
Undefined is another special value in JavaScript. When a variable is declared but not initialized, its value is undefined, because no value was given to that variable, not even the value null.
const pineapples;
console.log(pineapples);
undefined
Each primitive data type has a use-case and it's important to know when to use each one.