Flash Prevent Digonal Movement

I am trying to design my first flash game in unity I am have my player moving around but i don't want it to be able to move diagonally and my code is allowing it.

 package  
 {
     import flash.display.*;
     import flash.events.*;
     import fl.motion.easing.Bounce;
     
     
     public class Game extends MovieClip
     {
         //variables
         private var player:Player; //code ref movie
         private var speed:int; // referenc to speed
         
         private var left:Boolean; // controles left
         private var right:Boolean; // controles right
         private var up:Boolean; // controles up
         private var down:Boolean; // controles down
 
         public function Game():void 
         {
             // focus on the stage
             stage.focus = stage;
             
             // listen for keyboard events
             stage.addEventListener(KeyboardEvent.KEY_DOWN,keyDownFunction);// looking for key to be pressed down
             stage.addEventListener(KeyboardEvent.KEY_UP,keyUpFunction);// looking  for key to be up
             
             // creat the player
             player = new Player(); // creates the new player
             player.x = 300; // movement limits
             player.y = 50; // movement limits
             addChild(player);
             
             // set the speed
             speed = 10;
             
             // main game loop
             stage.addEventListener(Event.ENTER_FRAME, gameLoop);
             
             
         }
         // game loop
         public function gameLoop(event:Event)
         
         {
             //keep the player within the bounds
             if(left == true)
             
             {
                 if(player.x>20)
                 {
                     player.x = player.x - speed;
                 }
                 else if (player.x <20)player.x = 20;
             }
             if(right == true)
             {
                 if(player.x < 580)
                 {
                     player.x = player.x + speed;
                 }
                 else if (player.x > 580) player.x = 580;
             }
             if(down == true)
             {
                 if(player.y < 380)
                 {
                     player.y = player.y + speed;
                 }
                 else if(player.y > 380) player.y = 380;
             }
             if(up == true)
             {
                 if(player.y> 20)
                 {
                     player.y = player.y - speed;
                 }
                 else if(player.y < 20) player.y = 20;
             }
         }
         
         
         //key pressed
         public function keyDownFunction(event:KeyboardEvent) // check if key is down
         
         {
             // go left
             if(event.keyCode == 65) //looking for it to be pressed key code to use that key
             {
                 left = true; // go left
             }
             // go right
             if(event.keyCode == 68)//looking for it to be pressed key code to use that key
             {
                 right = true; // go right
             }
             // go up
             if(event.keyCode == 87)//looking for it to be pressed key code to use that key
             {
                 up = true; // go up
             }
             //go down
             if(event.keyCode == 83)//looking for it to be pressed key code to use that key
             {
                 down = true; //  go down
             }
         }
         //key lifted
         public function keyUpFunction(event:KeyboardEvent) // check to see if he has been released
         
         {
             
             if(event.keyCode == 65)//looking for it to be released key code to use that key
             {
                 left = false; // dont go left
             }
             
             if(event.keyCode == 68)//looking for it to be released key code to use that key
             {
                 right = false; // dont go right
             }
             
             if(event.keyCode == 87)//looking for it to be released key code to use that key
             {
                 up = false; // dont go up
             }
             
             if(event.keyCode == 83)//looking for it to be released key code to use that key
             {
                 down = false; // dont go down
             }
         }
 
     }
     
 }