I have recently been alerted to an "error" by Visual Studio Code in the following snippet:
someDateObject.toLocaleDateString('de-DE', Travel.dateOptions));
someDateObject.toLocaleDateString('de-DE', Travel.dateOptions));
Where Travel.dateOptions is defined as such:
public static dateOptions = { year: 'numeric', month: '2-digit', day: '2-digit' };
This has been working fine for the better part of the last 2 years, but upon opening the class inside VSC recently, it displayed following error for Travel.dateOptions:
Argument of type '{ year: string; month: string; day: string; }' is not assignable to parameter of
type 'DateTimeFormatOptions'.
Types of property 'year' are incompatible.
Type 'string' is not assignable to type '"numeric" | "2-digit"'. ts(2345)
I am dead confused as to why. Is this possibly a bug with VSC? The code seems to work fine (and has worked fine the entire time) once compiled - and according to the documentation for Date::toLocaleDateString() what I'm doing here seems perfectly valid.
Any ideas?
When you initialize a class property with a literal such as public foo = { bar: 'a' }, its type becomes { bar: string }, even if you declare it as readonly. TypeScript on purpose doesn't make the type too strict ({ bar: 'a' }).
Method toLocaleDateString accepts an object whose key year must be of type 'numeric' or '2-digit', but yours is of type string.
To make the type of the initialized object more specific, use as const:
public static dateOptions = { year: 'numeric', month: '2-digit', day: '2-digit' } as const;
I've just hit the same problem, rather than redeclare the const as const (which feels like a code smell) I forced the variable type:
formatDT(sourceDate: Date) {
const options: Intl.DateTimeFormatOptions = { month: "long", day: 'numeric', year: 'numeric', hour: '2-digit', minute: "2-digit" };
return new Intl.DateTimeFormat("en-GB", options).format(new Date(sourceDate));
}
Following your code example you must explicitly declare the DateTimeFormatOptions data type for dateOptions
const dateOptions: Intl.DateTimeFormatOptions = {
year: 'numeric',
month: '2-digit',
day: '2-digit'
};
export const Travel = { dateOptions };
const someDateObject = new Date();
console.log(someDateObject.toLocaleDateString('de-DE', Travel.dateOptions));