What does JavaScript interpret `+ +i` as?

Question

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 simply adding to a string which is what caused it to convert. This, however, lead me to the question: what is going on here? I would have actually expected that to be a compiler error, but JavaScript (at least in Chrome) is just fine with it... it just basically does nothing. I created a little JSFiddle to demonstrate: Demo ``` var i = 5; var j = + +i; document.body.innerHTML = i === j ? 'Same' : 'Different'; ``` Anyone know what's actually occurring and what JavaScript is doing with this process? I thought maybe it would treat it like `++i`, but `i` doesn't increment, and you can even do it with a value (e.g., `+ +5`), which you can't do with `++` (e.g., `++5` is a reference error). Spacing also doesn't affect it (e.g., `+ + 1` and `+ +1` are the same). My best guess is it's essentially treating t…

Accepted Answer

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
```

What does JavaScript interpret `+ +i` as?

Solution

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