How to implement the logical assignment in destructuring assignment in javascript?

Question

destructuring assignment doesn't work for the field in one object holds a falsy value, as follow:

let { aaa = 123 } = { aaa: null }
console.log(aaa) // null

so, how to achive ||= in object destructuring assignment to implement such the field's destructed defalut value? like this:

let { aaa ||= 123 } = { aaa: null }
console.log(aaa) // 123

// it equals to
// let aaa = ({ aaa: null }).aaa || 123

Answer 1

So you cannot do what you are trying to do.

The destructuring assignment works as expected/specified. It is just that the default value only works when the destructured value is undefined .

You have to use the normal syntax for "falsy" values ( note : this includes undefined, false, 0, NaN etc. Extensive list at https://developer.mozilla.org/en-US/docs/Glossary/Falsy ).

let { aaa } = { aaa: null }
aaa ||= 123;

---

Quoting from MDN Destructuring assignment

for objects

Default values
A variable can be assigned a default, in the case that the value unpacked from the object is undefined .

for arrays

Default values
A variable can be assigned a default, in the case that the value unpacked from the array is undefined .

Answer 2

You can add a default value in this way

let obj = null        
{ obj1 } = { obj1: obj || 123 }

OR

try assigning values to an object using a constructor. In that way the destructuring would work fine:

class Obj1 {
  a: string
  b: number
  constructor(obj) {
    this.a = obj && obj.a || 'default a'
    this.b = obj && obj.b || 1 
  }
}

let obj = null
let obj1 = new Obj1(obj)

let {aaa} = {aaa: obj1}