javascript - 是否可以声明一个适用于数字和大整数的 typescript 函数？

Question

在普通的无类型 Javascript 中，编写一个可以对数字或 bigint 进行操作的函数并不难，具体取决于传入的参数:

const sumOfSquares = (a,b) => a*a + b*b;
sumOfSquares(3, 4); // returns 25
sumOfSquares(3n, 4n); // returns 25n
sumOfSquares(3n, 4); // throws a TypeError

似乎应该有一种方法可以在 typescript 中声明这个函数，以便编译器强制参数一起工作。我试过了

const sumOfSquares = <N extends bigint | number>(a: N, b: N): N =>
  a * a + b * b;

但是编译器拒绝了这一点:

semantic error TS2322: Type 'number' is not assignable to type 'N'.
  'number' is assignable to the constraint of type 'N', but 'N' could be instantiated with a different subtype of constraint 'number | bigint'.

是否有不同的方法来编写类型声明以便它可以工作？

Answer 1

重载有用吗？

function isBigInt(a: bigint | number): a is bigint {
  return typeof (a) === 'bigint'
}

function isNumber(a: bigint | number): a is number {
  return typeof (a) === 'number'
}

function doSomething(a: bigint, b: bigint): bigint;
function doSomething(a: number, b: number): number;
function doSomething(a: bigint | number, b: bigint | number): bigint | number | never {
  if (isBigInt(a) && isBigInt(b))
    return a + b;
  else if (isNumber(a) && isNumber(b))
    return a + b;
  throw 'error';
}

let a = doSomething(1, 1)
let b = doSomething(1n, 1n)
let c = doSomething(1n, 1)