@ryusei/light/src/js/utils/object/assign/assign.ts

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import { isObject, isUndefined } from '../../type/type';
import { forOwn } from '../forOwn/forOwn';


/**
 * Assign U to T.
 *
 * @typeParam T - An object to assign to.
 * @typeParam U - An object to assign.
 *
 * @return An assigned object type.
 */
export type Assign<T, U> = Omit<T, keyof U> & U;

export function assign<T extends object>( object: T ): T;

// There is a way to type arguments recursively, but these fixed definitions are enough for this project.
export function assign<T extends object, U extends object>( object: T, source: U ): Assign<T, U>;

export function assign<T extends object, U1 extends object, U2 extends object>(
  object: T, source1: U1, source2: U2
): Assign<Assign<T, U1>, U2>;

export function assign<T extends object, U1 extends object, U2 extends object, U3 extends object>(
  object: T, source1: U1, source2: U2, source3: U3
): Assign<Assign<Assign<T, U1>, U2>, U3>;

/**
 * Assigns all own enumerable properties of all source objects to the provided object.
 * `undefined` in source objects will be skipped.
 *
 * @param object  - An object to assign properties to.
 * @param sources - Objects to assign properties from.
 *
 * @return An object assigned properties of the sources to.
 */
export function assign<T extends object, U extends object>( object: T, ...sources: U[] ): any {
  sources.forEach( source => {
    if ( isObject( source ) ) {
      forOwn( source, ( value, key ) => {
        if ( ! isUndefined( source[ key ] ) ) {
          object[ key ] = source[ key ];
        }
      } );
    }
  } );

  return object;
}