14 Using decorators

This chapter covers

Defining and applying decorators
Decorating classes, methods, properties, accessors, and auto-accessors
Using decorator context data
Creating decorators with a factory function
Accumulating state data in decorators

Decorators are a forthcoming addition to the JavaScript language that transform features defined by classes. TypeScript has long supported an experimental version of decorators, used mainly in Angular development, but TypeScript 5 has added support for the version of decorators that will be adopted in a future release of the JavaScript specification. Table 14.1 summarizes the chapter.

Table 14.1 Chapter summary (view table figure)

Problem	Solution	Listing
Transform a class feature	Define and apply a decorator	9–12, 16–30, 38–41
Get details of the feature to be transformed	Use the decorator context object	13–15
Configure each application of a decorator	Use a factory function	31–37
Perform initial setup for a decorator	Use an initializer function	42–44
Accumulate state data	Define a variable outside of the decorator function or factory function	45, 46

For quick reference, table 14.2 lists the TypeScript compiler options used in this chapter.

14.1 Preparing for this chapter

14.2 Understanding decorators

14.2.1 Using decorator context data

14.2.2 Using specific types in a decorator

14.3 Using the other decorator types

14.3.1 Creating a class decorator

14.3.2 Creating a field decorator

14.3.3 Creating an accessor decorator

14.3.4 Creating an auto-accessor decorator

14.4 Passing an additional argument to a decorator

14.5 Applying multiple decorators

14.6 Using an initializer

14.7 Accumulating state data

Summary