+
This addition operator servers two purposes: one for mathematical equations and one for concatinating strings.
Another weird example of addition happens when you add a boolean to a number.
console.log(1 + true); // 2
This happens because in computer-speak, true represents a 1 and false represents a 0. Remember the video game consoles of the old days (Playstation 2) specifically or even modern computer power supplies, there is a "1" and a "0" on the power switch to represent on and off.
In our example, true is actually a "1". Just to further explain this, look at this example showing how false is used.
console.log(1 + false); // 1
If a number and a string are used together, they actually behave a little differently.
console.log(1 + "1"); // 11
It literally adds the number to the string.