The logical OR operator (||) in JavaScript accepts two operands. If its left-side operand is truthy, then it will return that immediately; otherwise, it will evaluate and return the right-side operand:

0 || 1; // => 1
2 || 0; // => 2
3 || 4; // => 3

Much like the && operator, the || operator is flexible in that it does not cast what it returns to Boolean, and it evaluates in a short-circuited manner, meaning that it only evaluates the right-hand side operand if the left-side operand meets a condition—in this case, if the right-side operand is falsy:

true || thisWillNotExecute();
false || thisWillExecute();

Conventionally, a programmer may assume that the logical OR operator is akin to the question Are either A or B true? but in JavaScript, it is more akin to: If A is falsy, then give me B; otherwise, I'll settle for A. If we were to implement this operation ourselves, it might look something like this:

function or(a, b) {
  if (a) return a;
  return b;
}

Just as with &&, this means that || can be used flexibly to provide control flow or to evaluate specific expressions conditionally:

const nameOfUser = user.getName() || user.getSurname() || "Unknown";

As such, it should be used cautiously in a way that considers what readers of the code are familiar with, and in a way that considers all prospective operands and the resulting values from the operation.