singlebang.js

const x = 'abc'; // Coerces to true in a boolean context
const y = null; // Coerces to false in a boolean context
// "!" Creates a boolean context and returns the opposite.
const a = !x; // Value a is opposite of x, false.
const b = !y; // Value a is opposite of y, true.
if (a) {
  // NOT executed.
}
if (b) {
  // Executed.
}