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
			}
		}

	}
	
}

Consider working through more tutorials - this is very basic.

Don’t set up or down to true unless left and right are false. (or vice-versa).