Specification Type

A Specification Type对应于在算法中用于描述ECMAScript语言构造和ECMAScript Language Type语义的元值。

A Specification Type值是规范工件(仅仅是规范)，不一定对应于ECMAScript实现中的任何特定实体。

A Specification Type值可用于描述ECMAScript表达式计算的中间结果，但此类值不能存储为对象的属性或ECMAScript语言变量的值。

A Specification Type有以下几项Records：

Completion Record
Reference Record
List Record
Property Descriptor
Environment
Abstract Closure
Data Block

CompletionRecord

Completion Record 规范类型用于解释值和控制流的运行时传播，例如执行非本地控制传输的语句（break、continue、return和throw）的行为。

定义了以下的字段：

Field Name	Value	Meaning
`[[Type]]`	NORMAL, BREAK, CONTINUE,RETURN OR THROW	发生时的完成类型
`[[Value]]`	任何值除了一个Completion Record	产生的值
`[[Target]]`	a String or EMPTY	定向控制转移的目标标签。

以下速记术语有时用于指完成记录

normal completion refers to any Completion Record with a [[Type]] value of NORMAL.
break completion refers to any Completion Record with a [[Type]] value of BREAK.
continue completion refers to any Completion Record with a [[Type]] value of CONTINUE.
return completion refers to any Completion Record with a [[Type]] value of RETURN.
throw completion refers to any Completion Record with a [[Type]] value of THROW.
abrupt completion refers to any Completion Record with a [[Type]] value other than NORMAL.
a normal completion containing some type of value refers to a normal completion that has a value of that type in its [[Value]] field.

ECMAScript规范中定义的可调用对象仅返回normal completion或throw completion。返回任何其他类型的完成记录都被视为编辑错误。