Web Browser Arduino Simulation

As a first step click "Create a new circuit". Check Breadboard+Arduino circuit as Circuit Type.

Connect an LED on each digital pin 2-13 with the anodes (bend side of the LED). Connect the cathodes to each other and then to a resistor to the Arduino GND. Set the resistor value to 300 Ohm.  

Note: In the 123D Circuits breadboard view if the LED is pointing up the cathodes are the pins on the LEFT.  In this figure the anodes and cathodes of all the LEDs appear to be connected, this is not true, overlapping wires only connect at their endpoints.

Select the Arduino and click on the bottom of the page on "Arduino code editor" and add the following code:

int i = 2;
int time = 200;
int dir = 1;
// the setup routine runs once when you press reset:
void setup() {               
  // initialize the digital pin as an output.
    for(i=2;i<=13;i++){
  pinMode(i, OUTPUT);
  }   
}

// the loop routine runs over and over again forever:
void loop() {
  digitalWrite(i, HIGH);  
  delay(time);              
  digitalWrite(i, LOW);   
  i+=dir;            
  if(i<2|i>13){
  dir*=-1;
  i+=dir*2;
  } 
}