Should JavaScript use a header file format (a la WebIDL) to define its standard library?

header.jsidl

@namespace
class Math {
  static abs(x: Number): Number;  // Types optional; provide cast on input and assertion on ouptut    

  @nonwritable
  static LOG10E: Number;

  // ...
}

@legacyPrototypeInstance
class Date {
  // Overloads not included in JSIDL syntax
  @callable
  @length(7)
  constructor();

  static parse(str: String): Date;

  @length(7)
  static UTC( year: Number, @optional month: Number, @optional date: Number, @optional hours: Number, @optional minutes: Number, @optional seconds: Number, @optional ms: Number) : Number;

  [[DateValue]];  // Internal slot declaration
  
  [@@toPrimitive]();
  getHours(): Number;
  setHours(hour: Number, @optional min: Number, @optional sec: Number, @optional ms: Number): Number;
  // ...
} 

@namespace
class Intl {
  // Complex type Locales calls CanonicalizeLocaleList as its cast
  static Array getCanonicalLocales(locales: Locales);
} 

@dictionary
class DateTimeFormatOptions {
  @optional weekday: String;
  @optional year: String;
  @optional month: String;
  @optional day: String;
  @optional hour: String;
  @optional minute: String;
  @optional second: String;
  // ...
} 

@namespace(Intl)
class DateTimeFormat {
  @legacyIntlBoundMethod
  resolvedOptions();
  
  static supportedLocalesOf(locales: Locales): Array;
  
  get [@@toStringTag](): String;
  formatToParts(date: Date): Array;
  
  @legacyIntlBoundMethod
  @legacyIntlMethodFallback
  format(date: Date): String;

  @legacyIntlMethodFallback
  resolvedOptions(): DateTimeFormatOptions;

  @legacyIntlConstructFallback
  constructor(@optional locales: Locales, @optional options: DateTimeFormatOptions);

  [[InitializedDateTimeFormat]];
  [[Locale]];
  [[Calendar]];
  [[NumberingSystem]];
  [[TimeZone]];
  [[Weekday]];
  [[Era]];
  [[Year]];
  [[Month]];
  [[Day]];
  [[Hour]];
  [[Minute]];
  [[Second]];
  [[TimeZoneName]];
  [[HourCycle]];
  [[Pattern]];
  [[BoundFormat]];

  static [[AvailableLocales]];
  static [[RelevantExtensionKeys]];
  static [[LocaleData]];
}