Why does {} + [] return 0 in Javascript?
javascript
Solution
When there is a `{` at the beginning of a statement, it will be interpreted as a block, which may contain zero or more statements. An block with no statements in it will have an empty continuation value.
In other words, in this case, `{}` is interpreted as an empty code block.
The statement ends after the ending brace `}`, which means that the next three characters `+[]` comprise a statement of their own.
At the beginning of an expression or statement, `+` is the unary plus operator, which coerces its operand to a number.
So `+[]` is the same as `Number([])`, which evaluates to `0`.
In short, `{} + []` is an empty code block followed by an array coerced to a number.
All that said, if you evaluate `{} + []` inside an expression, it will return what you expect:
>> ({} + [])
"[object Object]"
Another interesting thing is that you cannot begin a statement with an object literal because the interpreter will try to parse it as a statement. Doing this
{ "object": "literal" };
will throw a syntax error.
Problem
Possible Duplicate: What is the explanation for these bizarre JavaScript behaviours mentioned in the 'Wat' talk for CodeMash 2012? I know that when `[]` is coerced to a string it returns the empty string (`""`), and when `{}` is coerced to a string it returns `"[object Object]"`. When I run `[] + {}` in my browser's Javascript console, it returns as I would expect: ``` >> [] + {} "[object Object]" ``` But when I run `{} + []`, it returns a completely unexpected value: ``` >> {} + [] 0 ``` What could be causing it to return `0`?