javascript - 为什么括号中的加号运算符的工作方式不同？

Question

您能解释一下为什么结果不同吗？

1. ({} + {})//= "[object Object][object Object]"
2. {} + {}//= NaN

我知道在这两种情况下对象都会转换为字符串，但为什么在第二种情况下结果会转换为数字？

Answer 1

来自:

http://www.2ality.com/2012/01/object-plus-object.html

The problem is that JavaScript interprets the first {} as an emptycode block and ignores it. The NaN is therefore computed by evaluating+{} (plus followed by the second {}). The plus you see here is not the binary addition operator, but a unary prefix operator that convertsits operand to a number, in the same manner as Number()

...

Why is the first {} interpreted as a code block? Because the completeinput is parsed as a statement and curly braces at the beginning of astatement are interpreted as starting a code block. Hence, you can fixthings by forcing the input to be parsed as an expression:

({} + {})

'[object Object][object Object]'