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Part I: Core JavaScript > Data Types and Values

Chapter 3. Data Types and Values

Computer programs work by manipulating values , such as the number 3.14 or the text "Hello World". The types of values that can be represented and manipulated in a programming language are known as data types, and one of the most fundamental characteristics of a programming language is the set of data types it supports. JavaScript allows you to work with three primitive data types: numbers, strings of text (known as "strings"), and boolean truth values (known as "booleans"). JavaScript also defines two trivial data types, null and undefined, each of which defines only a single value.

In addition to these primitive data types, JavaScript supports a composite data type known as object. An object (that is, a member of the data type object) represents a collection of values (either primitive values, like numbers and strings, or composite values, like other objects). Objects in JavaScript have a dual nature: an object can represent an unordered collection of named values or an ordered collection of numbered values. In the latter case, the object is called an array . Although objects and arrays are fundamentally the same data type in JavaScript, they behave quite differently and will usually be considered distinct types throughout this book.


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