Nested object assignment in Node.js

Question

Suppose I have an object (baz) of variable contents. How can I assign a sub-object (foo) with a key (baz) to that object in one line?

Examples:

var baz = {}
baz.foo.bar = 1;
console.assert(baz === { foo: { bar: 1 } });

(or, in the case where foo is already defined)

var baz = { foo: { 1: "b" } };
baz.foo.bar = 1;
console.assert(baz === { foo: { 1: "b", bar: 2 } });

Noting here that yes, I can easily write a function where I can use nestedAssign(baz, "foo", "bar", 2), but I am looking for a built-in solution. — wibbuffey
– wibbuffey, Commented Dec 27, 2021 at 0:26
It isn't entirely clear to me what you're trying to do and why. Are you looking for Object.assign()? Some sort of spread operator? — Brad
– Brad, Commented Dec 27, 2021 at 0:29

CertainPerformance · Accepted Answer · 2021-12-27 00:29:05Z

1

It's possible to put all in one line, though personally I wouldn't recommend it. You're technically doing two pretty different things:

Assign an object as a property if the object doesn't exist yet
Assign a property if the object already exists, mutating the existing object

You can assign baz.foo or the empty object to baz.foo, then assign the bar property value to the resulting object:

const baz = {};
(baz.foo ??= {}).bar = 1;
console.log(baz.foo.bar);

const baz2 = {};
(baz2.foo ??= {}).bar = 1;
console.log(baz2.foo.bar);

I'd prefer

// Create the object if it doesn't exist yet
baz.foo ??= {};
// Assign the new nested value
baz.foo.bar = 1;

Code readability is more important than golfing in most cases.

answered Dec 27, 2021 at 0:29

CertainPerformance

373k55 gold badges354 silver badges359 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

wibbuffey Over a year ago

Valid point, I was looking to do it in 1 line to make it more readable while less verbose. This seems to work just as well, much better than writing an existing function to do this.

krirkrirk · Accepted Answer · 2021-12-27 00:29:32Z

0

For the first case :

baz.foo = {bar :1}

And your code works for the second case

(Note that the following code outputs false :

a = {b:1}
console.log(a==={b:1})

)

answered Dec 27, 2021 at 0:29

krirkrirk

4571 gold badge3 silver badges9 bronze badges

Collectives™ on Stack Overflow

Nested object assignment in Node.js

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related