[allstars]

prova detta istället:

var fix_height = function() {
   var w = window.innerWidth;
   var h = window.innerHeight;

     var canvas_left_blue = document.getElementById('canvas_left_blue');
     var canvas_right_yellow = document.getElementById('canvas_right_yellow');

     canvas_left_blue.style.height = h + "px";
     canvas_right_yellow.style.height = h + "px";

     console.log(h);

 }
 window.onload = fix_height();
 window.addEventListener('resize', function(event){
  fix_height();
});

Fast jag håller med om att istället använda flexbox!