function pick( obj, keys ) {
	var out;
	var key;
	var i;
	if ( typeof obj !== 'object' || obj === null ) {
		throw new TypeError( format( 'invalid argument. First argument must be an object. Value: `%s`.', obj ) );
	}
	out = {};
	if ( isString( keys ) ) {
		if ( hasOwnProp( obj, keys ) ) {
			out[ keys ] = obj[ keys ];
		}
		return out;
	}
	if ( isStringArray( keys ) ) {
		for ( i = 0; i < keys.length; i++ ) {
			key = keys[ i ];
			if ( hasOwnProp( obj, key ) ) {
				out[ key ] = obj[ key ];
			}
		}
		return out;
	}
	throw new TypeError( format( 'invalid argument. Second argument must be either a string or an array of strings. Value: `%s`.', keys ) );
}
Returns a partial object copy containing only specified keys. If a key does not exist as an own property in a source object, the key is ignored.

@param {Object} obj - source object
@param {(string|StringArray)} keys - keys to copy
@throws {TypeError} first argument must be an object
@throws {TypeError} second argument must be either a string or an array of strings
@returns {Object} new object

@example
var obj1 = {
    'a': 1,
    'b': 2
};

var obj2 = pick( obj1, 'b' );
// returns { 'b': 2 }