TypeScript and type aliases

Question

As I know TypeScript allows to create aliases for any types. Such as:

type MyNum = number;
var y: MyNum;
y = 33; // it's ok

but the followong code is not valid:

type MyType = Object;
const dt = new MyType(); // here is an error: 'MyType only refers to a type, but is being used as a value here'

Where am I wrong and how could I create instance of MyType?

Answer 1

Type aliases are only for compile time, they are not getting translated into the compiled javascript code.

Your first code compiles to:

var y;
y = 33;

As you can see, there's nothing here about MyNum.

However, in your 2nd code snippet you're trying to use MyType as a value and not just as a type.
The compiler won't allow that because at runtime MyType isn't present as it compiles to:

var dt = new MyType();

Type aliases, just like interfaces (and types in general) are used for compilation only, so you cannot use them as values.

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Edit

To create an instance of MyType, in this case:

const dt1: MyType = {};
const dt2: MyType = new Object();
const dt3: MyType = Object.create({});