Aliases with the Structural Behavior of TypeScript

The structural nature of TypeScript

TypeScript is a structural language and not a nominal language. This means that TypeScript compares the structure and not the name of an object to determine if the objects are similar.

The following code has a function that takes an anonymous type that has a property name. The example has three ways to call the function:

1. interface
2. type
3. anonymous object

It works in all three scenarios because they have the exact shape needed.

In the following code, there is MyTypeA that defines a schema for an object with a single member name on line 2. On line 4, the type is the same which is also equivalent to the anonymous parameter on line 6.

Lines 10-11 define the two types and lines 12-13 invoke the function, even if it’s not the anonymous parameter. It works because they have the same structure. TypeScript is not a nominal but a structural language. Hence, on line 14, the function can also be invoked.