CODEWITHSUNDEEP
javascriptoperatorsnumber-literal
Mutation Person
Mutation Person

Reputation: 30520

Why is it only valid syntax to perform property access on a numeric literal when a space precedes the dot (`.`) operator?

The following JavaScript code:

console.log(2 .toString());

Outputs “2”.

(Note: The space between the '2' and '.x' is intended)

Simple question: Why? Especially when the following yield syntax errors:

console.log(2.toString());
console.log(2. toString());

Upvotes: 4

Views: 122

Answers (1)

Pointy
Pointy

Reputation: 413996

The . is an operator. The 2 is a number. The x is (treated as) a property name.

A floating-point numeric constant must not have embedded spaces. Thus, 2 .x is an expression calling for the constant 2 to be promoted to a Number object, and then the property called "x" is examined. There isn't one, of course, so the value is undefined.

You can get the same effect a little more explicitly with

alert((2).x);

Note that

alert("Hello".x);

is somewhat similar: in that case, it's not a numeric constant, it's a string constant. It's less peculiar because there's no syntactic funny business involved, but otherwise the interpreter does similar things when evaluating. The string constant is first converted to a String object, and then the "x" property is fetched.

edit — to clarify a little, 2.x is an error because it's parsed as a numeric constant ("2.") followed by the identifier "x", and that's a syntax error; two values placed next to each other like that with no intervening operator do not form any sort of construct in the language.

Upvotes: 8

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