useful-copy/index.js

useful deep/shallow copy/update

	function copy( target, source, no_overwrite ) {
		no_overwrite = no_overwrite === true;

		if ( !source ) {
			source = target;
			target = {};
		}

		source = Object( source );

		for ( var key in source )
			if ( Object.prototype.hasOwnProperty.call( source, key ) && ( no_overwrite !== true || !Object.prototype.hasOwnProperty.call( target, key ) ) )
				target[key] = source[key];

		return target;
	}

	function is_plain_object( item ) {
		if ( item === UNDEF || item === null || typeof item !== 'object' )
			return false;

		var proto = Object.getPrototypeOf( item );

		return !!( proto === null || proto.constructor === Object );
	}

	function merge( target, source ) {
		if ( source === UNDEF ) {
			if ( target === UNDEF ) // todo: test
				return  target;

			if ( Array.isArray( target ) )
				return  target.reduce( merge_array, [] );

			else if ( is_plain_object( target ) )
				return  Object.keys( target ).reduce( merge_object, {
							source : target,
							target : {}
						} ).target;

			return target;
		}

		if ( Array.isArray( source ) ) {
			if ( !Array.isArray( target ) )
				target = [];
			else
				target.length = source.length; // remove any extra items on the merged Array

				return source.reduce( merge_array, target );
		}
		else if ( is_plain_object( source ) )
			return  Object.keys( source ).reduce( merge_object, {
						source : source,
						target : is_plain_object( target ) ? target : {}
					} ).target;

		return source;
	}

	function merge_array( target, source, i ) {
		target[i] = merge( target[i], source );

		return target;
	}

	function merge_object( o, key ) {
		o.target[key] = merge( o.target[key], o.source[key] );

		return o;
	}

	function update( target, source ) {
		if ( source === UNDEF )
			return merge( target );

		if ( target === UNDEF || target === null )
			return merge( source );

		if ( Array.isArray( source ) ) {
			if ( !Array.isArray( target ) )
				return target;

			return source.reduce( update_array, target )
		}
		else if ( is_plain_object( source ) ) {
			if ( !is_plain_object( target ) )
				return target;

			return Object.keys( source ).reduce( update_object, { source : source, target : target } ).target;
		}

		return target;
	}

	function update_array( target, source, i ) {
		target[i] = update( target[i], source );

		return target;
	}

	function update_object( o, key ) {
		o.target[key] = update( o.target[key], o.source[key] );

		return o;
	}

	var UNDEF;

	module.exports = copy;
	copy.merge     = merge;
	copy.update    = update;