Always get a value~ Popular concepts ~

JavaScript by default has no type definitions. It has been like that since day one. Today we can solve that by using languages like TypeScript. However, as we mentioned a few chapters back, those solutions work at build time. When our code runs in the browser, we still have to deal with the good old vanilla JavaScript.

Let's say that we face a situation where we really must have value. For the functions, this means setting up a default value like so:

function calculate(value = 0) {
  return value * 2;
}

For everything else, we may use the logical OR operator:

const user = { age: 37 };
const name = user.firstName || "unknown";
console.log(name);

These two options work if we have a default value. But what if we don't have one, and we have to force the developer to pass an argument. We can do it via this neat trick.

const required = () => {
  throw new Error("Please provide a number.");
};
const calculate = (value = required()) => {
  return value + 42;
};
console.log(calculate(8)); // 50
console.log(calculate(28)); // 70
calculate(); // throws error