📙 This article is part of the Javascript Deep Dive series.
So, what data types does Javascript have?
The two main categories are: primitives and objects (non-primitives).
In this part we will cover the primitives and in the next one the objects.
Dynamic Types 🌊
Javascript is a dynamically typed language. When you assign a value to a variable you don't specify the type and you can reassign any value to it.
var x = 1;
x = "abc";
The type of a variable will be decided at runtime rather than compile time like statically languages such as C++ or Java.
Typeof 🔎
You can use the typeof operator to find the type of an element.
> typeof "abc"
'string'
> typeof 123
'number'
> typeof {x:1}
'object'
Primitives ⛰
Primitives in Javascript are types that simply hold a value.
String 🅰
Strings hold textual data. They are basically a list of chars.
In Javascript unlike C++ there is no char type for you to hold only one character. In a string variable you can hold no chars or as many as you want (theoretically the limit is 2^53 - 1 chars which is really big number, unlikely reachable in 99.999% percent of cases)
Strings are represented as 16-bit lists of unsigned integers.
They are indexed from 0.
The length of a String is the number of characters in it. You can access it with .length.
You can use single quotes (' '), double quotes (" ") or back quotes (` `).
var s = "";
console.log(s.length);
s = "abc";
console.log(s.length);
Number 🥇
Numbers hold all kinds of numeric values.
Unlike Java where there are types like int,double, float and more to represent integers and floating point numbers, Javascript uses the number type as an umbrella for all of them.
They are represented as double precision floating point values. Double precision means that they use 64-bits instead of 32-bits the the single floating point precision uses.
More info about double precision can be found on this wiki page: Double-precision floating-point format
The values range between -2^53 - 1 → 2^53 - 1.
To get the maximum value use Number.MAX_VALUE.
> Number.MAX_VALUE
1.7976931348623157e+308
To get the minimum value use Number.MIN_VALUE.
> Number.MIN_VALUE
5e-324
There are two three symbolic values that have the number type: NaN ,Infinity and -Infinity.
NaN
NaN means "Not a Number".
> typeof NaN
'number'
It's used to represent unsuccesfull operations with a number or conversions from a non-number type to a number.
> 'a' / 2
NaN
> parseInt('a')
NaN
Any operation with NaN is a NaN.
> NaN + 1
NaN
> NaN * NaN
NaN
> NaN - 'abc'
NaN
> NaN / false
NaN
Infinity
Infinity is a property available on the global scope that represents the infinity value. It is treated as larger than any other number.
The property is initialized to Number.POSITIVE_INFINITY value.
It's note the same as Number.MAX_VALUE.
> Infinity > 3
true
> Infinity > Number.MAX_VALUE
true
If the result of an operation is too large to contain in memory then it will be shown as Infinity.
> Math.pow(2, 10000)
Infinity
An operation on Infinity results either to Infinity ,-Infinity , 0 or NaN.
> Infinity + 1
Infinity
> Infinity * -1
-Infinity
> Math.pow(2, Infinity)
Infinity
> Math.pow(0.3, Infinity)
0
> Math.pow(1, Infinity)
NaN
> 0 * Infinity
NaN
Division to zero of a non-negative number gives Infinity.
> 1/0
Infinity
-Infinity
-Infinity is the negative equivalent of Infinity.
The property is initialized to Number.NEGATIVE_INFINITY value.
It's note the same as Number.MIN_VALUE.
> Infinity < 3
true
> Infinity < Number.MIN_VALUE
true
It behaves equivalently to Infinity.
> Math.pow(2, -Infinity)
0
> -Infinity * 2
-Infinity
> -Infinity + 1
-Infinity
> -Infinity * Infinity
-Infinity
> -Infinity * -Infinity
Infinity
> Math.pow(0.3, -Infinity)
Infinity
> Math.pow(1, -Infinity)
NaN
BigInt 🎈
BigInt can work with values beyond the limits of number. (-2^53 - 1 → 2^53 - 1)
You create a big int by adding n at the end of the number.
> typeof 2n
'bigint'
> 2n ** 53n
9007199254740992n
> 2n ** 53n + 1n
9007199254740993n
BigInt works only with BigInt in arithmetic and bitwise operations.
> 3n + 1
Uncaught TypeError: Cannot mix BigInt and other types, use explicit conversions
> 3n + 3n
6n
> 3n >> 2
Uncaught TypeError: Cannot mix BigInt and other types, use explicit conversions
> 3n >> 2n
0n
The following arithmetic operators can be used: +, *, -, /, **, and % .
The following bit wise operators can be used: &, |, ~, ^, << and >>.
A BigInt is loosely equal to a number.
> 3n === 3
false
> 3n == 3
true
> 3n > 3
false
> 3n > 2
true
It works like a number when it's implicitly converted to boolean: if, ||, &&, Boolean, !
Boolean 🤥
TheBoolean type has only two values: true or false.
> typeof true
'boolean'
> typeof false
'boolean'
They are used and resulted in logical operations.
> 3 > 0
true
> 2 < 1
false
> "b" > "a"
true
Undefined 🤔
Undefined is a type that describes declared variables which have not yet been initialized with a value.
> var x
> console.log(x)
undefined
> typeof x
'undefined'
Null 📦
Null is a value that can be assigned to a variable to intentionally denote the absence of something.
> var x = null;
> console.log(x)
null
One quirk to notice here is that the typeof null gives object. This is regarded as a mistake which dates to the first implementations of Javascript.
> typeof null
'object'
Symbol 🎨
Symbol is a new addition to Javascript. It's a unique, immutable and anonymus value.
> const S = Symbol();
> console.log(S);
Symbol()
You can provide a debug description for the symbol.
> const S = Symbol("a");
> console.log(S);
Symbol("a")
Two symbols with the same description are not equal.
> const S1 = Symbol("a")
> const S2 = Symbol("a")
> S1 == S2
false
Every symbol will be unique ⇒ you can use them as keys for objects.
Symbols are not automatically converted to strings.
There is a global registry holding all the symbols. You can use Symbol.for() and Symbol.keyFor() to interact with the registry.
Sources 📚
Reach Out 👋
Was this helpful for you? Let me know what you think in the comments.
You can find me on Twitter and Github
