问题
As far as I understand, short-circuiting with the logical AND && operator works like the following:
Assuming I have the expressions a and b then a && b is the same as a ? b : a since
if a is truthy then the result will be b and
if a is falsy then the result will be a (without even trying to resolve b)
That being the case why is the following (demo) code throwing a SyntaxError:
var add = function(a,b) {
b && return a+b; // if(b) return a+b
...
}
Is there a way to short circuit with a return statement?
回答1:
The && binary operator needs both parts to be expressions.
return something is a statement but not an expression (it doesn't produce a value, as a value wouldn't be useful when the function ends).
Just use
if (b) return a+b;
with the added benefit of an easier to read code.
Read more :
- Expressions vs Statements
- the return statement (EcmaScript spec)
- logical operators (MDN)
回答2:
No, return is a statement, you cannot use it as a part of an AND expression.
You can transform your code to a single return statement though if you need that for some reason:
if (b) return a+b;
/* else */ ...
is (more or less) equivalent to
return b && a+b || (...);
Of course, in any code that you write by hand and read with your eyes, you should just an if statement anyway.
来源：https://stackoverflow.com/questions/34292255/short-circuit-with-a-return-statement