函数参数对象的解构导致未定义的变量

Question

I am running Node v6.6.0, which has support for destructuring function arguments:

function foo ({ a: { b }}) {
  // stuff
}

Suppose I want to destructure and access both a and b . Sadly the following doesn't seem to work:

function foo ({ a: { b }}) {
  return [a, b]
}
foo({ a: { b: 123 }})
// ReferenceError: a is not defined!

Is this bug in Node or is this the expected behavior for ES6? Shouldn't both a and b be defined in the function? If not, why does destructuring have the effect of un-defining a base property name ( a )?

Is there a way I can use parameter destructuring to get both a and b defined in the function? I'm explicitly trying to avoid manually destructuring them.

Answer 1

Is this bug in Node or is this the expected behavior for ES6?

This is expected behaviour. Because {a: {b}} doesn't bind a as a name it just indicates you want to access a property of the destructured object.

You could use the following.

 function foo ({ a, a: {b} }) { return [a, b] } console.log(foo({ a: { b: 123 }}))