如何在 Typescript 中进行动态签名和返回类型？

Question

I want to create a function behave like getter and setter based on if argument present. The logic is already in the function, but TS can not figure the type out and complains.

// if no argument, is a getter, and return `Coord` type
cursor(): Coord

// if present, is a setter, return `this` type
cursor(p: Coord): this

cursor(p){
  if (arguments.length === 0) return this._cursor
  this._cursor = p
  return this
}

Answer 1

You are very close. Your argument type for your method that has the implementation has to be compatible with all overloads. In this case you have account for the argument being optional.

cursor(): Coord
cursor(p: Coord): this
cursor(p?: Coord) { // p has to be optional
    if (arguments.length === 0) return this._cursor
    this._cursor = p!; // non-null assertion
    return this
}

Note that you also need a non-null assertion on p once you know it is defined.