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A value is an entity that can take on the personality of one of the implemented data types. Some types are reserved for internal use and are not generally made visible to the script developer although this may be implementation-dependent and they might be visible with a debugger.
The ECMA 262 standard defines nine data types. The host environment may add others depending on what it needs. The various types are listed in the table, which indicates whether they are special internal types:
| Type Name | Description |
|---|---|
| Aggregate | A collection of atomic types assembled collectively into an object. |
| Arithmetic | All types that yield a value that can be operated on numerically. |
| Array | Collections of objects and identifiers assembled into a sequence. |
| Basic | The fundamental simple, non-object types. |
| Boolean | This type can store and yield true or false values. |
| Completion | Used only as the intermediate result of expression evaluations and cannot be stored in object properties. |
| List | Used only as the intermediate result of expression evaluations and cannot be stored in object properties. |
| Null | This has exactly one value, null, and is distinct from undefined. |
| Number | Integer and floating point values are all stored in a generic number type. |
| Object | An object is an unordered collection of properties. Each property consists of a name, a value and a set of attributes. |
| Reference | Used only as the intermediate result of expression evaluations and cannot be stored in object properties. |
| Scalar | The non-object types. |
| String | Strings are arrays of characters which are accessible individually by indexing their position in the sequence. |
| Undefined | This value is returned by variables that have not yet been assigned a value. |
You cannot access values of type Reference, List and Completion from your scripts and they cannot be stored as object properties.
| See also: | Aggregate type, Boolean, Cast operator, Completion type, const, enum, Identifier, int, List type, Logical operator, null, Number, Object, Reference, Scalar type, String, undefined type |
ECMA 262 edition 2 - section - 4.3.1
ECMA 262 edition 2 - section - 8
ECMA 262 edition 3 - section - 4.3.1
ECMA 262 edition 3 - section - 8
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JavaScript Programmer's Reference, Cliff Wootton Wrox Press (www.wrox.com) Join the Wrox JavaScript forum at p2p.wrox.com Please report problems to support@wrox.com © 2001 Wrox Press. All Rights Reserved. Terms and conditions. | ||