var INIT_SZ, MAX, MIN;

var init = function() {
    INIT_SZ = 13;
    MAX = 15;
    MIN = 11;  
    var elem = document.getElementsByTagName("body");
    elem[0].style.fontSize = 13;
}

var enlarge = function() { 
var elem = document.getElementsByTagName("body");
var size = parseInt(elem[0].style.fontSize.replace("px", ""));
if(size < MAX)
 {  
  elem[0].style.fontSize = (size + 1) + "px";       
 }
}   
  
var shrink = function(){  
var elem = document.getElementsByTagName("body");   
var size = parseInt(elem[0].style.fontSize.replace("px", "")); 
if(size > MIN) {  
   elem[0].style.fontSize = (size - 1) + "px"; 
   }    
}