Question 252213 in Javascript Question posted in
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Javascript – Setting nested object property when parent can be undefined?

If I want to set a nested property like foo.bar.baz = true but it’s parent foo.bar might be undefined, what’s the best way to do that?

I know I can do this with:

foo.bar = {
  ...foo.bar,
  baz: true
}

but is there a more concise way of doing it?

Thanks!

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3

Answers


  1. 0

    Works as it is:

    const foo = {};

foo.bar = {
  ...foo.bar,
  baz: true
};

console.log(foo);
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  2. 0

    You could do:
    foo.bar = Object.assign(foo.bar ?? {}, { baz: true }).

    Also I wouldn’t consider spread operator used with variables that might be undefined as a good practice (although your snippet code won’t end up with run time error).

    So either way do foo.bar ?? {} or ...(foo.bar ?? {})

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  3. 0

    You could use the nullish coalescing assignment (??=)operator:

    (foo.bar ??= {}).baz = true;

    But in my opinion, it’s not very readable, and your original code is easier to read. A more readable of the above would be to use:

    foo.bar ??= {};
foo.bar.baz = true;

    This is a bit different to your original code, as it will keep the original object reference in foo.bar if it already exists, as opposed to always creating a new one.

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