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02-3-datatypes.md

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2.3 Datatypes

Computers store data in binary format - i.e. 0s and 1s.
That is grouped into bytes.

Humans on the other hand, do not understand bytes or binary directly. We
understand numbers like 1, 20, 42 (which are whole numbers), or 23.4, 10/4,
(which are decimals or fractions). We understand letters of the alphabet like
A or g, and words formed by these alphabets like nyan and cat.

Fortunately, most programming platforms, allow us to use datatypes more human-readable
than plain bits and bytes.

Some common data formats computer programming languages support are -

Data type Description Examples
integer whole numbers -1, 0, 15
float decimal numbers or rational fractions -2.5, 0.1, 22.3334
character a single literal. could be a letter or a number or a symbol 'a', 'B', '4', '/'
string a sequence of characters 'word', 'o em gee'
boolean a 2-value data that can be truthy or falsy true, false
array an iterative sequence. each item of an array could be any of the above data types [1,2,3], ['a', 'e', 'i']

2.3.2 Datatypes in Javascript

In Javascript we have following datatypes -

Data Type Description Examples
number Any numerical value. Does not distinguish between whole numbers and fractions 1, 43.22, -0.5
string Any array of characters, (JS by default supports UTF-8 charset, so all characters of a string must in UTF-8). There is no character datatype, so single characters are also strings "hello", "a", "wow !", "this is str 2"
boolean A value which is either true or false true, false
undefined A special datatype in Javascript for 'undefined' data. An undefined type basically means there is no data in it. It is similar (but not exactly same) to 'void' datatype in C-like programming languages undefined
function In Javascript functions themselves are first-class objects. So a function is also a variable. The type of such variables which are functions is function function a () {return "a"}
object Pretty much everything that can be classified into any of the above datatypes, is an object. All types extend from the object type in Javascript. Arrays and null are also of the type object {a: 10, b:20}, [1,3,4]

2.3.2.1 Finding Datatype of object in Javscript

We can find the data type of an object in Javascript using the typeof operator.

var a = 10, 
    b = 'str', 
    c = [3,4,1], 
    d = {P:1, Q:2}, 
    e = null, 
    f = false,
    g = function () { return 0} ;

console.log(typeof a) // "number"
console.log(typeof b) // "string"
console.log(typeof c) // "object"
console.log(typeof d) // "object"
console.log(typeof e) // "object"
console.log(typeof f) // "boolean"
console.log(typeof g) // "function"
console.log(typeof undefined) // "undefined"

2.3.2.2 Type "strictness" in Javascript

While data has type in Javascript, the variables do not enforce types strictly. Which makes Javascript a loosely typed language.

What this essentially means is that unlike languages like C/C++ or Java, where writing int a = 10 makes a an integer variable, and in future you cannot write something like a = false to assign a boolean to it , in Javascript, doing something similar is perfectly valid.

var a = 10;
console.log(typeof a) //"number"
a = "hello there"
console.log(typeof a) //"string"

{% hint style='working' %} NOTE that values always have types. 10 is number. 'hello' is string. Being loosely typed means the variable (i.e. the LHS) has no type strictly defined. That is a container 'a' which contained the value 10, can at some point of time in future contain the value 'hello'. Thus, the container 'a' does not constrain itself from containing any type of data. {% endhint %}