JavaScript nested object default value

Question

So if I have an object defined like so:

var object = {
    prop1: 'val1',
    prop2: 'val2',
    prop3: {
         subprop1: 'subval1',
         subprop2: 'subval2',
         subprop3: 'subval3'
    }
}

What I am wondering is if there is a way to set a "default" value so if I call:

object.prop3

I do not want to get:

Object {subprop1: "subval1", subprop2: "subval2", subprop3: "subval3"}

Instead I would like:

defaultsubval

Any help would be appreciated.

What exactly are you trying to achieve? Do you want to implement a custom property getter? — p.s.w.g, Jun 21 '14 at 18:13
@p.s.w.g I would prefer something as inline as possible... for example I would love if I could do this: var object = { prop: 'defaultval' { subprop: 'subval' } }; But I know I cannot do that... — godismyjudge95, Jun 21 '14 at 18:15
No this can't be done. How would it ever know when you access `object.prop3` whether or not you're stopping there for the default or you're going to actually grab a property from the object? And if you did continue with another property, should it come from the object or the default value you returned? — cookie monster, Jun 21 '14 at 18:17
@cookiemonster Maybe look ahead and see if there is a request for a sub object? I really have no idea how, if at all, this would be written. — godismyjudge95, Jun 21 '14 at 18:19
@LeinardoSmtih: How would it know that the request for a property on the result of `object.prop3` is supposed to come from the default value or the sub object? I'm just explaining why this can't be done. — cookie monster, Jun 21 '14 at 18:20
@cookiemonster As I was saying it could maybe "look ahead" and see if there is a request for the sub object. So before it parses object.prop3 it would look to see if any of the sub properties are being requested (object.prop3.subprop1, etc) — godismyjudge95, Jun 21 '14 at 18:23
@LeinardoSmtih - javascript just doesn't work that way. You're asking for `var x = object.prop3; console.log(x.subprop1);` to show something different than `console.log(object.prop3.subprop1)`. JS just doesn't do that. You could supply a method to the `object.prop3` object that would get a default value, but you'd have to call that method or rely on a `.toString()` implicit call to retrieve it. — jfriend00, Jun 21 '14 at 18:52

score 0 · Answer 1 · edited May 23 '17 at 12:03

0

As both cookie monster and jfriend00 above noted. This is impossible with just the object notation. Javascript just does not work that way. However, I found an alternate way of doing the same thing by Getting the name of a requested subobject

edited May 23 '17 at 12:03

Community

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answered Jun 21 '14 at 19:41

godismyjudge95

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score 0 · Answer 2 · answered Feb 28 '20 at 12:03

Here's how it can be done using Symbol's toPrimitive:

const myTheme = {
  prop1: 'val1',
  prop2: 'val2',
  color: {
    darker: 'orange',
    lighter: 'white'
  }
}

Object.defineProperty(myTheme.color, Symbol.toPrimitive, {
  value: () => 'yellow'
});

so, we got something like:

console.log('primary color: ' + myTheme.color.darker) // returns "primary color: orange"
console.log('primary color: ' + myTheme.color) // returns "primary color: yellow"

JavaScript nested object default value

2 Answers2