The logical OR operator (||) evaluates the left operand using JavaScript truthiness. It returns that value when truthy; otherwise, it returns the right-hand fallback. section 3.3.2
Supplying a default city
An unassigned variable has the value undefined, so the fallback is selected: let firstCity; let secondCity = firstCity || "London";. The result is London. section 3.3.2
Use || carefully when zero, an empty string, NaN, or false are meaningful values. Each is falsy, so the fallback replaces it. A zero tax rate therefore becomes 10% in the example. section 3.3.2
