Add simulated nominal type for COM SAFEARRAY and VarDate to lib.scripthost.d.ts

[zspitz]

TypeScript Version: nightly (2.5.0-dev.20170725)

When running Javascript under an Automation context (Windows Script Host, or HTML Applications), there are two types exposed by various APIs: VarDate and SafeArray. These types have no shape from Javascript's perspective:

• they cannot be constructed using new, and
• they have no members that can be consumed from Javascript

However, other methods/constructors/properties expect these types and will fail if an incorrect type is passed in:

var rst = new ActiveXObject('ADODB.Recordset');
// open the connection and recordset here
var fields = ['firstname', 'lastname'];
var values = ['Plony', 'Almony'];

// Will fail at runtime, since two SafeArrays are expected, and not two Javascript arrays
rst.Update(fields, values);

Currently, VarDate is typed in lib.scripthost.d.ts as an empty interface; while SafeArray has no defined type, and methods that expect a SafeArray are typed with any (example).

I propose adding a representation of these types to lib.scripthost.d.ts:

declare class VarDate {
    private VarDate_typekey: VarDate;
    private constructor();
}

declare class SafeArray<T = any> {
    private SafeArray_typekey: SafeArray<T>;
    private constructor():
}

• An interface couldn't be used here, because there is no shape from Javascript, and an empty interface is equivalent to any

• The private constructor prevents new VarDate();

• The other private member prevents assigning an arbitrary object to a variable/parameter of this type:

    //compiler error -- Property 'VarDate_typekey' is missing in type '{}'
   let x: VarDate = {};
  

Note that this is actually simulating nominal typing (thanks @Aleksey-Bykov for the suggestion). If some form of nominal typing is introduced to TypeScript, the definitions for VarDate and SafeArray could be rewritten accordingly.

---

The previous definition for Update could then be written as follows:

declare namespace ADODB {
    interface Recordset {
        Update(Fields: SafeArray<string>, Values: SafeArray): void;
    }
}

---

VBArray and Enumerator could be modified to take advantage of the generic type of SafeArray, as in this commit.

[zpdDG4gta8XKpMCd]

that article is a bit outdated, here is the latest workaround: #202 (comment)

[zspitz]

@Aleksey-Bykov Fixed, thanks.

[zspitz]

@DanielRosenwasser Any news? Could you describe some of the discussion relating to this?