JavaScript（ES6）：命名参数和默认值

Question

Coming from Python and really liking the way to set named parameters and default values - now it seems that ES6 allows me to do similar. But I can't see why this last call breaks:

fun = ({first=1, last=1}) => (1*first+2*last)

console.log("-----------")

console.log( fun({first:1, last:2}) )

console.log("-----------")

console.log( fun({last:1, first:2}) )

console.log("-----------")

console.log( fun() ) // Breaks

Answer 1

You need a default object.

 var fun = ({ first = 1, last = 1 } = {}) => 1 * first + 2 * last; // ^^^^ console.log(fun({ first: 1, last: 2 })); console.log(fun({ last: 1, first: 2 })); console.log(fun()); 

Answer 2

因为你需要一个可以解构的对象：

fun({})