Mapbox Load After resize -

i have problem mapbox map - when reload page, map on website have small dimensions. (cca 50x100); after when resize window, map full loading.

i glad advice, ps: sorry english.

my code : in index.php

<div id='map'></div> 

in js :

l.mapbox.accesstoken = '-accestoken-';     var map = l.mapbox.map('map', 'id_map');     maxzoom: 18     map.invalidatesize();