Types

Computers are sophisticated and can make use of more complex variables than just numbers. This is where variable types come in. Variables come in several types and different languages support different types.

The most common types are:

Numbers
- Float: a number, like 1.21323, 4, -33.5, 100004 or 0.123
- Integer: a number like 1, 12, -33, 140 but not 1.233
String: a line of text like "boat", "elephant" or "damn, you are tall!"
Boolean: either true or false, but nothing else
Arrays: a collection of values like 1, 2, 3, 4, 'I am bored now'
Objects: a representation of a more complex object
null: a variable that contains null contains no valid Number, String, Boolean, Array, or Object
undefined: the undefined value is obtained when you use an object property that does not exist or a variable that has been declared but has no value assigned to it.

JavaScript is a “loosely typed” language, which means that you don't have to explicitly declare what type of data the variables are. You just need to use the var keyword to indicate that you are declaring a variable, and the interpreter will work out what data type you are using from the context, and use of quotes.

The typeof operator is used to checking the datatypes of a variable.

typeof "John"                 // Returns "string"
typeof 3.14                   // Returns "number"
typeof NaN                    // Returns "number"
typeof false                  // Returns "boolean"
typeof [1,2,3,4]              // Returns "object"
typeof {name:'John', age:34}  // Returns "object"
typeof new Date()             // Returns "object"
typeof function () {}         // Returns "function"
typeof myCar                  // Returns "undefined" *
typeof null                   // Returns "object

Data types used in JavaScript can be differentiated into two categories based on containing values.

Data types that can contain values:

string
number
boolean
object
function

Object, Date, Array, String, Number, and Boolean are the types of objects available in JavaScript.

Data types that cannot contain values:

null
undefined

A primitive data value is a simple data value with no additional properties and methods and is not an object. They are immutable, meaning that they can't be altered. There are 7 primitive data types:

string
number
bigint
boolean
undefined
symbol
null

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Last updated 2 years ago

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typeof "John" // Returns "string" typeof 3.14 // Returns "number" typeof NaN // Returns "number" typeof false // Returns "boolean" typeof [1,2,3,4] // Returns "object" typeof {name:'John', age:34} // Returns "object" typeof new Date() // Returns "object" typeof function () {} // Returns "function" typeof myCar // Returns "undefined" * typeof null // Returns "object