1. Exposition

How did the men in the ambush see the javelin if they were far away?

Joshua 8:19 (ESV)

19 And the men in the ambush rose quickly out of their place, and as soon as he had stretched out his hand, they ran and entered the city and captured it. And they hurried to set the city on fire.

The sword/javelin may well have had some kind of a flag on top, which could then be seen from far away. Most likely some scouts relayed the message to the ambush force.1