Using the switch(true) Pattern in JavaScript

[Costas]

// https://seanbarry.dev/posts/switch-true-pattern

//before

if (!user) {
  throw new Error("User must be defined.");
} else if (!user.firstName) {
  throw new Error("User's first name must be defined");
} else if (typeof user.firstName !== "string") {
  throw new Error("User's first name must be a string");
} else if (// ... lots more validation here)


//after

switch (true) {
  case !user:
    throw new Error("User must be defined.");
  case !user.firstName:
    throw new Error("User's first name must be defined");
  case typeof user.firstName !== "string":
    throw new Error("User's first name must be a string");
  default:
    return user;
}