What Does JavaScript Interpret `+ +i` As?

An interesting thing I've never seen before was posted in another question. They had something like: var i = + +1; They thought the extra + converted it to a string, but they were

Solution 1:

Putting your the statement through the AST Explorer, we can see that what we get here is two nested Unary Expressions, with the unary + operator.

It's a unary expression consisting of + and +i, and +i is itself a unary expression consisting of + and i.

The unary expression with the unary + operator, will convert the expression portion into a number. So you're essentially converting i to a number, then converting the result of that to a number, again (which is a no-op).

For the sake of completion, it works on as many levels as you add:

var i = 5;
console.log(+ + + + + +i); // 5
console.log(i); // still 5

Solution 2:

It's in the specification.

Digging through, we can see from §14.6.2.2 that the increment and decrement operators are listed before (and should be preferred) over the unary operators. So precedence alone won't explain this.

Looking up the the punctuation table in §11.7, we can see that every single instance of ++ (the operator) in the spec shows the two together, without whitespace. That's not conclusive, until you check...

The whitespace rules in §11.2, specifically:

White space code points may occur within a StringLiteral, a RegularExpressionLiteral, a Template, or a TemplateSubstitutionTail where they are considered significant code points forming part of a literal value. They may also occur within a Comment, but cannot appear within any other kind of token.

JS does not allow arbitrary whitespace mid-operator.

The JS syntax in both PegJS and Esprima corroborate this, matching on the literal two-character string ++.

Solution 3:

For me it's very clear;

var a = +3;
var b = +a; // same as a, could be -a, for instance
var c = + +a; // same as above, same as +(+a)

Solution 4:

If you do ++variable the javascript interpreter sees it as the increment operator.

If you do + +variable the javascript interpreter sees it as Unary plus, coercing the value to a number, twice.

So

var a = 1;
var b = +a;
var c = +b;

console.log(c);// still 1

is the same as

var c = + +1;

So the simple answer is that two plus signs can not be separated by a space to be interpreted as incrementation, the space makes it so the interpreter sees two seperate spaces, which is what it really is

Solution 5:

The + operators converts into a number, two + operators with a space in between does nothing additional.