
Object-Oriented JavaScript - Second Edition
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Any value that you use is of a certain type. In JavaScript, there are just a few primitive data types:
Number: This includes floating point numbers as well as integers. For example, these values are all numbers: 1
, 100
, 3.14
.
String: These consist of any number of characters, for example "a"
, "one"
, and "one 2 three"
.
Boolean: This can be either true
or false
.
Undefined: When you try to access a variable that doesn't exist, you get the special value undefined
. The same happens when you declare a variable without assigning a value to it yet. JavaScript initializes the variable behind the scenes with the value undefined
. The undefined data type can only have one value – the special value undefined
.
Null: This is another special data type that can have only one value, namely the null
value. It means no value, an empty value, or nothing. The difference with undefined
is that if a variable has a value null
, it's still defined, it just so happens that its value is nothing. You...
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