JSでMAPを実現する

function Map() {    
 var struct = function(key, value) {    
  this.key = key;    
  this.value = value;    
 }    
     
 var put = function(key, value){    
  for (var i = 0; i < this.arr.length; i++) {    
   if ( this.arr[i].key === key ) {    
    this.arr[i].value = value;    
    return;    
   }    
  }    
   this.arr[this.arr.length] = new struct(key, value);    
 }    
     
 var get = function(key) {    
  for (var i = 0; i < this.arr.length; i++) {    
   if ( this.arr[i].key === key ) {    
     return this.arr[i].value;    
   }    
  }    
  return null;    
 }    
     
 var remove = function(key) {    
  var v;    
  for (var i = 0; i < this.arr.length; i++) {    
   v = this.arr.pop();    
   if ( v.key === key ) {    
    continue;    
   }    
   this.arr.unshift(v);    
  }    
 }    
     
 var size = function() {    
  return this.arr.length;    
 }    
     
 var isEmpty = function() {    
  return this.arr.length <= 0;    
 }    
   
 this.arr = new Array();    
 this.get = get;    
 this.put = put;    
 this.remove = remove;    
 this.size = size;    
 this.isEmpty = isEmpty;    
}