ai logic in javascript

Now that it has come to ai logic im competently stumped, how would i include logic that places an ai bid with a 50/50 chance of placing a bid if the player places a bid. thanks.

 #pragma strict
 var information: String; 
 private var guiOn = false;
 private var rect: Rect;
 var btnTexture : Texture;
 var ClosePostion : Vector2 = new Vector2 (200,5);
 var CloseSize : Vector2 = new Vector2 (35,35);
 var CloseIcon : Texture;
 var MyString = "";
  
  
 //click to open gui
 function OnMouseDown(){
     guiOn = true; 
     rect = Rect(Input.mousePosition.x, Input.mousePosition.y, 300, 100);
     yield WaitForSeconds(500);
     guiOn = false;
 }
  
 function OnGUI(){
     if (guiOn){
        GUI.Box(Rect(0,0,200,200),"Current bid");
        if (!btnTexture) {
          Debug.LogError("Assign a texture");
          return;
        }
  
        if (GUI.Button(Rect(10,10,50,50),btnTexture))
          Debug.Log("texturebutton");
  
  
        if (GUI.Button(Rect(10,70,50,30),"Bid")) {
          var bid : int;
          if (!int.TryParse(MyString, bid))
           bid = 0;
  
          Debug.Log("The bid was: "+bid);
        }
  
        var temp = "";
  
         for (var c : char in MyString) {
             if (c >= "0"[0] && c <= "9"[0]) {
                 temp += c;
                 }
             } 
  
         MyString = temp;
         MyString = GUI.TextField(new Rect(10,130,180,20),MyString,30);
  
         //close button
         if (GUI.Button(Rect(160,2,CloseSize.x,CloseSize.y),CloseIcon)) {
             guiOn = false;
        }
     }
 }