JavaScript 2.0 Core Language Expressions

Thursday, November 11, 1999

Most of the behavior of expressions is the same as in JavaScript 1.5. Differences are highlighted below. One general difference is that most expression operators can be overridden via operator overloading.

Identifiers

The above keywords are not reserved and may be used in identifiers.

Just like in ECMAScript Edition 3, an identifier evaluates to an internal data structure called a reference. However, JavaScript 2.0 references have several additional attributes, one of which is a namespace. The namespace is set to the value of the ParenthesizedExpression. If the ParenthesizedExpression is a simple Identifier or QualifiedIdentifier then the parentheses may be omitted.

Primary Expressions

A Number literal or ParenthesizedExpression followed by a String literal is a unit expression. The unit object specified by the String is looked up; the result is called as a function and passed two arguments: the numeric value of the Number literal or ParenthesizedExpression, and either null (if a ParenthesizedExpression was provided) or the original Number literal expressed as a string.

The string representation allows user-defined unit classes to define extended syntaxes for numbers. For instance, a long-integer package might define a unit called "L" that treats the Number literal as a full 64-bit number without rounding it to a double first.

A ? Identifier expression is used to access scope information.

Function Expressions

Object Literals

Array Literals

Postfix Unary Operators

The @ operator performs a type cast. The second operand specifies the type. Both the . and the @ operators accept either a QualifiedIdentifier or a ParenthesizedExpression as the second operand. If it is a ParenthesizedExpression, the second operand of . must evaluate to a string. a.(x) is a synonym for a[x] except that the latter can be overridden via operator overloading.

The [] operator can take multiple (or even named) arguments. This allows users to define data structures such as multidimensional arrays via operator overloading.

An ArgumentList can contain both positional and named arguments. Named arguments use the same syntax as object literals.

Prefix Unary Operators

Multiplicative Operators

Additive Operators

Bitwise Shift Operators

Relational Operators

Equality Operators

Binary Bitwise Operators

Binary Logical Operators

The ^^ operator is a logical exclusive-or operator. It evaluates both operands. If they both convert to true or both convert to false, then ^^ returns false; otherwise ^^ returns the unconverted value of whichever argument converted to true.

Conditional Operator

Assignment Operators

Expressions

Type Expressions

Waldemar Horwat Last modified Thursday, November 11, 1999