A signature using union type does not produce the same invalid usages than a signature using union types

[stof]

Bug Report

The handbook recomments using overloads rather than a union when only the argument type changes. But this does not produce the same behavior regarding catching extra object literal properties.

🔎 Search Terms

overload, argument, union

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about type system

⏯ Playground Link

Playground link with relevant code

💻 Code

interface RgbColor {
  red: number;
  green: number;
  blue: number;
  alpha?: number;
}

interface HslColor {
  hue: number;
  saturation: number;
  lightness: number;
  alpha?: number;
}

interface HwbColor {
  hue: number;
  whiteness: number;
  blackness: number;
  alpha?: number;
}
export class SassColorOverload {
  constructor(color: RgbColor);
  constructor(color: HslColor);
  constructor(color: HwbColor);
  constructor(color: RgbColor | HslColor | HwbColor) {
    // TODO
  }
}
export class SassColorUnion {
  constructor(color: RgbColor | HslColor | HwbColor) {
    // TODO
  }
}
new SassColorOverload({
  red: 255,
  green: 255,
  blue: 255,
  hue: 0,
  saturation: 0,
  lightness: 100,
})
new SassColorUnion({
  red: 255,
  green: 255,
  blue: 255,
  hue: 0,
  saturation: 0,
  lightness: 100,
})

🙁 Actual behavior

SassColorOverload reports an invalid object literal, but SassColorUnion does not.

🙂 Expected behavior

Same behavior regarding catching extra properties in object literals when using the union type, especially given that this is the recommended implementation in https://www.typescriptlang.org/docs/handbook/declaration-files/do-s-and-don-ts.html#use-union-types

[MartinJohns]

Duplicate of #20863.

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.