Combining melted chocolate with eggs
The cocoa butter in your chocolate melts fully at 43 degrees Celsius (110 F). But it stays liquid until at least 30 degrees C (85 F). 
The most heat sensitive proteins in an egg white coagulate at around 65 degrees C (145 F), most proteins stay stable until 85 degrees C (185 F). 


As you shouldn't overheat your chocolate anyway, you have a certain temperature range where the chocolate will stay liquid, yet the egg unaffected. 

Note that the real problem and culinary art therefore is not the coagulating egg, but the effect of warm chocolate on any "foam" you might have produced in an earlier step: Too warm, and the bubbles might pop, too cool and the chocolate will harden as the cool other ingredients take up too much heat before it is fully incorporated.

Rule of thumb:
Melt the chocolate gently and let cool until barely warm to the touch. Stir quickly, yet gently, when incorporating the liquid chocolate into your batter.
(And read the recipe in case you need to deviate from this.)