Filter object properties by key

This chapter follows Defining object properties in JavaScript.

You have a record of nested objects and need a shallow copy without one key—or only a subset of keys. Rest destructuring and Object.fromEntries keep the source object intact.

Drop one key with rest destructuring

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const data = {
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  item1: { key: 'a', value: 'b' },
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  item2: { key: 'c', value: 'd' },
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  item3: { key: 'e', value: 'f' },
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};
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const { item2, ...newData } = data;

When the key name is in a variable:

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const key = 'item2';
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const { [key]: _removed, ...newData } = data;

The _removed binding holds the omitted value; only newData is returned to callers.

Allowlist with Object.fromEntries

For several allowed keys, filter entries then rebuild the object:

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const raw = {
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  item1: { key: 'a' },
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  item2: { key: 'b' },
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  item3: { key: 'c' },
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};
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const allowed = ['item1', 'item3'];
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const filtered = Object.fromEntries(
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  Object.entries(raw).filter(([key]) => allowed.includes(key)),
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);

This is a shallow copy: nested objects are shared with raw. For denylists, invert the predicate: !denied.includes(key).

Small utility

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function pick(obj, keys) {
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  const set = new Set(keys);
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  return Object.fromEntries(
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    Object.entries(obj).filter(([k]) => set.has(k)),
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  );
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}
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function omit(obj, key) {
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  const { [key]: _, ...rest } = obj;
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  return rest;
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}

Prefer pick/omit at module boundaries so API shapes stay explicit in TypeScript.

Next: Prototypes and inheritance.