function makeArray(n) { 
  this.length = n; 
  for (var i=1; i<=n; i++) { 
  this[i] = ""; 
  } 
  return this; 
} 
var i;
var taille= 10; 
function imagealeatoire() { 
  i = Math.floor(taille * Math.random() + 1); 
  return image[i]; 
} 

image = new makeArray(taille); 
var j = 1;
while(j<=taille){
  image[j]="header"+j+".jpg";
  j++;
}