为什么数字文字不能访问Number方法？ [英] Why don't number literals have access to Number methods?

问题描述

如果查看ECMAScript 3规范，您会看到原始值类型Null和Undefined没有附带Null和Undefined对象。

If you look at the ECMAScript 3 specification you will see that primitive value types Null and Undefined don't have accompanying Null and Undefined Objects.

>> Null
ReferenceError: Null is not defined

其他原始值类型Number，String和Boolean类型确实包含可以从全局范围引用的Number，String和Boolean对象。

The other primitive value types Number, String and Boolean types do have accompanying Number, String and Boolean objects which you can reference from global scope.

>>Number
function Number() { [native code] }
>>Boolean
function Boolean() { [native code] }

这些原语的目的值类型是为各自的原始值类型提供 toString 和 valueOf 等方法：

The purpose for these primitive value types is to provide methods such as toString and valueOf for their respective primitive value types:

>>var n = 1;
>>n.toString();
"1" 

与

>>var n = 1;
>>Number.prototype.toString.call(n);
"1"

布尔值和字符串也是这样的：

Booleans and strings also work that way:

>>var b = true;
>>b.toString(); 
"true"
>>Boolean.prototype.toString.call(b);
"true"

您可以看到原始值对象正在使用它们的方法当您尝试混合类型时，伴随对象：

You can see that the primitive value objects are using the methods of their accompanying object when you try to mix types:

>>Boolean.prototype.toString.call(n); 
TypeError: Boolean.prototype.toString is not generic
>>Number.prototype.toString.call(b)
TypeError: Number.prototype.toString is not generic

有趣的是，对于布尔值和字符串文字类型，您可以直接从文字中调用这些方法：

Interestingly enough for boolean and string literal types, you can call these methods directly from the literal:

>>true.toString();
"true"
>>Boolean.prototype.toString.call(true)
"true"
>>"moo".toString();
"moo"
>>String.prototype.toString.call("moo")
"moo"

原始值null和undefined，因为它们没有伴随Null和Undefined对象不能做这些事情：

Primitive values null and undefined, since they don't have accompanying Null and Undefined objects cannot do these things:

>>Null
ReferenceError: Null is not defined
>>null.toString()
TypeError: Cannot call method 'toString' of null

原始值类型编号的行为类似于两者的混合。如果你直接使用Number的原型对象的方法，你可以在文字上调用 toString ：

Primitive value type number behaves like a mix of the two. You can call toString on a literal if you directly use the Number's prototype object's method:

>>Number.prototype.toString.call(1);
"1"

但你不能像文字一样从文字中访问该方法字符串和布尔值：

But you cannot access the method from the literal itself like you can with strings and booleans:

>>1.toString()
SyntaxError: Unexpected token ILLEGAL

为什么数字文字的行为与boolean和string的行为不同，即使有一个Number对象？

Why is it that number literals behave differently from boolean and string even though there's a Number object?

推荐答案

你可以以相同的方式访问它，这是一个不同的解析问题，要做到这一点，使用稍微不同的语法：

You can access it the same way, it's a different parsing issue here, to do it, use a slightly different syntax:

(1).toString()

数字可以有小数，所以当你去解析代码，使用括号有效时，以小数结尾的语法有点模棱两可。当你看到这也是有效的时候会更清楚：

Numbers can have decimals, so the syntax for ending in a decimal is a bit ambiguous when you go to parse the code, use parenthesis to be valid. It's a bit clearer when you see that this is also valid:

(1.).toString()

然而只有 1.toString（）它试图解析为带有小数的数字，它会失败。

However with just 1.toString() it's trying to parse as a number with a decimal, and it fails.

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