@feugene/mu/src/object/defaults.ts

Helpful TS utilities without dependencies

import clone from '~/core/clone'
import isObject from '~/is/isObject'

/**
 * Assigns own and inherited enumerable string keyed properties of source
 * objects to the destination object for all destination properties that
 * resolve to `undefined`. Source objects are applied from left to right.
 * Once a property is set, additional values of the same property are ignored.
 *
 * **Note:** This method mutates `object`.
 *
 * @example
 *
 * defaults({ 'a': 1 }, { 'b': 2 }, { 'a': 3 });
 * // => { 'a': 1, 'b': 2 }
 */

export default function defaults(
  origin: Record<PropertyKey, any>,
  ...destinations: Record<PropertyKey, any>[]
): Record<PropertyKey, any> {
  const ln = destinations.length

  let i = 0,
    object,
    key,
    value,
    sourceKey

  for (; i < ln; i++) {
    object = destinations[i]
    if (!isObject(object)) {
      continue
    }
    for (key in object) {
      value = object[key]
      if (value && value.constructor === Object) {
        sourceKey = origin[key]
        if (sourceKey && sourceKey.constructor === Object) {
          defaults(sourceKey, value)
        } else {
          origin[key] = clone(value)
        }
      } else {
        if (!Object.prototype.hasOwnProperty.call(origin, key)) {
          origin[key] = value
        }
      }
    }
  }

  return origin
}