ECMAScript 4 Netscape Proposal Core Language Statements

Wednesday, June 4, 2003

Statements

Most of the behavior of statements is the same as in ECMAScript 3. Differences are highlighted below.

A Substatement is a statement directly contained by one of the compound statements label:, if, switch, while, do while, for, or with (but not a block). A substatement cannot be a directive except that, in non-strict mode only, it can be a var definition without attributes or types.

A substatement can also consist of one or more attributes applied to a group of substatements enclosed in braces. The attributes must evaluate to either true or false. The braces do not form a scope in this case.

The Semicolon productions allow both grammatical and line-break semicolon insertion.

Empty Statement

Expression Statement

Super Statement

The super statement calls the superclass’s constructor. It can only be used inside a class’s constructor.

Block Statement

A block groups statements and forms a scope.

Labeled Statements

If Statement

The semicolon is optional before the else.

Switch Statement

Do-While Statement

The semicolon is optional before the closing while.

While Statement

For Statements

A for statement forms a scope. Any definitions in it (including the ForInitializer and ForInBinding) are visible inside the for statement and its substatement, but not outside the for statement. However, a var definition inside a for statement may be hoisted to the nearest enclosing regional scope.

With Statement

Continue and Break Statements

Return Statement

A return statement can only be used inside a function or constructor. The return statement cannot have an expression if used inside a constructor or a setter.

Throw Statement

Try Statement

Each CatchClause forms a scope. The Parameter, if any, is defined as a local variable visible only within the CatchClause.

The Blocks following try and finally are also scopes like other Block statements.

Directives

Attributes can be applied to a group of directives by following them by a {, the directives, and a }. The attributes apply to all of the enclosed directives. The attribute true is ignored. The attribute false causes all of the enclosed directives to be omitted. When used this way, the braces do not form a block or a scope.

Annotated groups are useful to define several items without having to repeat attributes for each one. For example,

class foo {
  var z:Integer;
  public var a;
  private var b;
  private function f() {}
  private function g(x:Integer):Boolean {}
}

is equivalent to:

class foo {
  var z:Integer;
  public var a;
  private {
    var b;
    function f() {}
    function g(x:Integer):Boolean {}
  }
}

Programs

Waldemar Horwat Last modified Wednesday, June 4, 2003