safe-spread

safe-spread

A helper function that updates only the existing keys of an object in JS, deeply merging values without adding new keys.

• Works recursively on nested objects.
• Ignores keys that don’t exist in the base object.
• Can be written in immutable mode (returns a new copy) or mutable mode (updates the original object in place).

Usage

import { safeSpread } from "safe-spread";

const base = {
  a: 1,
  b: 2,
  c: {
    d: 4,
    e: 5,
  },
};

const update = {
  a: 10, // existing top-level key - will be updated
  bNew: 99, // NOT existing in base - will be ignored
  c: {
    d: 40, // existing nested key - will be updated
    f: 100, // NOT existing in base.c - will be ignored
  },
};

const result = safeSpread(base, update);

console.log(result);
//   {
//   a: 10,
//   b: 2,
//   c: {
//     d: 40,
//     e: 5
//   }
// }