Why don't number literals have access to Number methods? [duplicate]

This question already has answers here: Why can't I access a property of an integer with a single dot? (5 answers) Closed 4 years ago.

If you look at the ECMAScript 3 specification you will see that primit开发者_高级运维ive value types Null and Undefined don't have accompanying Null and Undefined Objects.

>> Null
ReferenceError: Null is not defined

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] }

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" 

is the same as

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

Booleans and strings also work that way:

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

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

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"

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

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"

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

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

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

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

(1).toString()

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()

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

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I think you'll find an answer to your question in this answer to another Stack Overflow question. To summarize Theo's answer:

[T]he parser expects a number followed by a dot to be a floating point literal. [...] [Y]ou only have to add another dot to make it work[.]

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Null (capital N) is a variable name. Reserved words are case sensitive. null is the object null. typeof null === "object" //true