[qwerty-клавиатура]

var pressed = [],
     left = 37,
     up = 38,
     right = 39,
     down = 40;

addEventListener( 'keydown', function(ev) {
    pressed[ev.keyCode] = 1;
} );

addEventListener( 'keyup', function(ev) {
    pressed[ev.keyCode] = 0;
} );

addEventListener( 'load', function() { if (pressed[left] && pressed[up]) {/*...*/} } );