Mastering TypeScript 3 - Third Edition

Explicit casting

As with any strongly typed language, there comes a time where you need to explicitly specify the type of an object. This concept will be expanded upon more thoroughly in the next chapter, but it is worthwhile making a quick note of explicit casting here. An object can be cast to the type of another by using the < > syntax.

This is not a cast in the strictest sense of the word; it is more of an assertion that is used at compile time by the TypeScript compiler. Any explicit casting that you use will be compiled away in the resultant JavaScript and will not affect the code at runtime.

Let's rewrite our previous sample, and use explicit casting, as follows:

var item1 = <any>{ id: 1, name: "item 1" }; 
item1 = { id: 2 }; 

Here, ...