[crooked-v]

A simple TypeScript example:

    interface DuckTypedObject {
      quack: true
      bark?: false
      eyes: 'beady'
    }

This will require that any object used as a DuckTypedObject must have the `quack` and `eyes` properties and may optionally have a `bark` of `false`, but doesn't otherwise prescribe what the object actually has to be.

[Scarbutt]

This is the best part of TS IMO (structural typing).

[ledauphin]

agreed 100%. structural, statically-checkable typing of objects is the best thing to happen for reusable and testable code in my programming lifetime.

[uk_programmer]

Sorry to be pedantic but that isn't quite right. I do use the same technique myself quite a lot with the options pattern.

However it is worth keeping the following in mind. The compiler will check that in your code that these properties are present and assigned correctly. However at runtime nothing is guaranteed especially when dealing with the DOM.

One of the things that I don't like about TypeScript (I have written a fair bit of it) is that you believe you have type safety when it is really type hinting.

[crooked-v]

Validation functions are pretty easy to write, as long as your data is being handled in a predictable way.

[uk_programmer]

Yes. However you can for example do the following in typescript:

    function someFunction(obj?:DuckType) {
        //Snip other logic
        someOtherFunction(obj);
    }

    function someOtherFunction(obj:DuckType) {

    }

The type checker catch that. So you still have to do:

    function someFunction(obj?:DuckType) {
        obj = obj || { /* set some object properties */
        //Snip other logic
        someOtherFunction(obj);
    }

    function someOtherFunction(obj:DuckType) {

    }

I have found plenty of examples where people haven't set a default value because the compiler hasn't flagged anything wrong with the code and you get an uncaught reference error.

[tome]

Huh, shouldn't the things on the right hand side of the colons be types not values?