Primitive Data Types
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.
JAVASCRIPTconst cars = 7;
console.log(cars);
BASH7
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.
JAVASCRIPTconst city = "New York City";
console.log("The greatest city in the world is " + city + ".");
HTMLThe 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).
JAVASCRIPTconsole.log(`Look how
cool this string is.
It is on multiple lines!`);
HTMLLook 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:
JAVASCRIPTconst restaurant = "Chipotle";
console.log(`My favorite restaurant is ${restaurant}!`);
HTMLMy favorite restaurant is Chipotle!
String interpolation is useful for inserting variables into strings and are 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.
JAVASCRIPTconst place = "Mexico City";
console.log(place.toLowerCase());
JAVASCRIPTmexico 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.
JAVASCRIPTconst place = "Mexico City";
console.log(place.toUpperCase());
JAVASCRIPTMEXICO 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:
JAVASCRIPTconst phrase = " time and";
const sentence = "I dominate in Fortnite" + phrase.repeat(3) + " time again.";
console.log(sentence);
HTMLI 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
:
JAVASCRIPTconst sentence = "The house is red.";
const newSentence = sentence.replace("red", "blue");
console.log(newSentence);
JAVASCRIPTThe 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:
JAVASCRIPTconst sentence = "The house is red.";
console.log(sentence.includes("house"));
console.log(sentence.includes("tiger"));
JAVASCRIPTtrue
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".
JAVASCRIPTconst 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:
JAVASCRIPTconst 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:
JAVASCRIPTfunction 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.");
HTMLThere are 6 shirts left in your size.
Sure, you could do this without using symbols like this:
JAVASCRIPTconst 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:
JAVASCRIPTconst 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.
JAVASCRIPTconst 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
.
JAVASCRIPTconst pineapples;
console.log(pineapples);
HTMLundefined
Each primitive data type has a use-case and it's important to know when to use each one.
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