Discriminate between empty object type and other concrete types

Question

All of this compiles without error:

interface Empty { }
interface MaybeEmpty { a?: number; }

var one: Object = 20;
var two: Empty = 21;
var three: {} = 22;
var          


        

Answer 1

Necromancing.
Had this problem myselfs.
This is actually possible in TypeScript 2.2+.

You need to add & object to your type-definition

e.g.

var varname: YourInterface & object = something;

in your case:

interface Empty { }
interface MaybeEmpty { a?: number; }
interface MaybeEmptyAndMore { a?: number; [x:string]: any; }


var one: Object = 20;
var two: Empty = 21;
var three: {} = 22;
var four: MaybeEmpty & object = 23;
var foura: MaybeEmpty & object = {};
var fourb: MaybeEmpty & object = { a: "23"};
var fourc: MaybeEmpty & object = { abc: "23"};
var fourd: MaybeEmptyAndMore & object = { abc: "123", def: "456" };

By the way, if it could be a string or an interface (object), then:

obj: string | YourInterface & object

e.g.

class Cookie
{
    constructor(nameOrSettings: string | ICookieSettings  & object )
    {
        if(typeof(nameOrSettings)  === 'string')
        { do_something();}
        else if(typeof(nameOrSettings) === 'object')
        {
             var obj:ICookieSettings = nameOrSettings;
        }
        else throw TypeError("foo");
    }
}