javascript - JavaScript typeof 曾经返回过 "array"吗？

Question

我在各种开源项目中看到过这个习语:

it instanceof Array || typeof it == "array"

我知道后半部分在 ECMAScript 5(或 6)中不可能为真，但是是否有从 typeof 返回“array”的实现？或者这是一个伪造的防御性编程案例？

Answer 1

不，至少从 ECMAScript 的第一个版本开始是这样。

ECMAScript 1 (1997 年 6 月)

11.4.3 - The typeof operator

The production UnaryExpression : typeof UnaryExpression is evaluated as follows:

1. Evaluate UnaryExpression.
2. If Type(Result(1)) is Reference and GetBase(Result(1)) is null, return "undefined".
3. Call GetValue(Result(1)).

4. Return a string determined by Type(Result(3)) according to the following table:

   • Undefined: "undefined"
   • Null: "object"
   • Boolean: "boolean"
   • Number: "number"
   • String: "string"
   • Object (native and doesn’t implement [[Call]]): "object"
   • Object (native and implements [[Call]]): "function"
   • Object (host): Implementation-dependent

ECMAScript 2 (1998 年 8 月)

没有变化。

ECMAScript 3 (1999 年 12 月)

无相关变化。

11.4.3 - The typeof operator

The production UnaryExpression : typeof UnaryExpression is evaluated as follows:

1. Evaluate UnaryExpression.
2. If Type(Result(1)) is not Reference, go to step 4.
3. If GetBase(Result(1)) is null, return "undefined".
4. Call GetValue(Result(1)).

5. Return a string determined by Type(Result(4)) according to the following table:

   • Undefined: "undefined"
   • Null: "object"
   • Boolean: "boolean"
   • Number: "number"
   • String: "string"
   • Object (native and doesn’t implement [[Call]]): "object"
   • Object (native and implements [[Call]]): "function"
   • Object (host): Implementation-dependent

ECMAScript 4

此规范已被放弃。