Decorator
A decorator is a programming-language construct that adds metadata or behavior to, or transforms, a program declaration, often a function or class.
Essential TypeScript 5, Third Edition
A decorator function is a function invoked when a decorator is applied and returns the replacement class feature.
- How it is used
- Transforms class features without editing their implementations and describes application building blocks in Angular.
- How deep it goes
- Works through method replacements, context data, generic constraints, class type limitations, factories, stacking order, and shared state.
- Examples
- Uses a timed method, a serializing subclass, stacked message decorators, accumulated timing data, and Angular module and component declarations.
- What you can do after
- Build it from scratch to wrap methods, configure each application, and recognize a class decorator’s TypeScript type limitation.
Read how Essential TypeScript 5, Third Edition explains decorator →
Python How-To
A decorator is a callable that modifies or extends the behavior of another callable or class without changing its underlying definition.
- How it is used
- Extracts shared behavior such as execution-time logging from multiple functions without adding it to each function body.
- How deep it goes
- Builds and dissects a function decorator as a closure, including argument forwarding, return values, and metadata preservation; defers full closure theory.
- Examples
- Demonstrates execution-time logging and metadata inspection, then proposes timing CSV-file and SQLite data operations.
- What you can do after
- Build it from scratch to add reusable logging while preserving arguments, return values, and function metadata.
The Well-Grounded Python Developer: How the pros use Python and Flask
A Python decorator is a callable construct that extends or modifies a function or method without changing its source definition.
- How it is used
- Uses decorators to preserve direct attribute access while adding coordinate checks, and to add timing around a function call.
- How deep it goes
- Works through property getters and setters plus a hand-written timing wrapper, without developing an exhaustive account of decorator behavior.
- Examples
- Shows a rectangle coordinate property and a timing decorator applied to a delayed task.
- What you can do after
- Apply it via Python’s `@property` and setter decorators to manage coordinates, or write a wrapper to time a function.
Read how The Well-Grounded Python Developer: How the pros use Python and Flask explains decorator →
Django in Action
A decorator is a Python language construct that associates additional behavior or metadata with a function or class.
- How it is used
- Turns Django view functions into API endpoints while attaching HTTP methods and endpoint configuration.
- How deep it goes
- Explains decorator syntax, route configuration, request flow, and registration, but does not descend into decorator implementation internals.
- Examples
- Uses a RiffMates hello endpoint and shows Router-to-NinjaAPI-to-Django URL registration.
- What you can do after
- Apply it via Django Ninja to build routed API endpoints with method, schema, naming, and authentication configuration.
The Joy of JavaScript
A wrapper-like construct that augments method behavior without changing the method's core implementation.
- How it is used
- Separates cross-cutting behavior from business logic through dynamically intercepted method calls.
- How deep it goes
- Explains object specifications, before-and-after actions, higher-order wrappers, and Proxy/Reflect wiring, but not decorator syntax.
- Examples
- Demonstrates Counter validation, credential tracing, password obfuscation, and composition of nested proxies.
- What you can do after
- Apply validation, tracing, logging, or return-value enhancement without modifying the decorated object’s business methods.
Build Python Web Apps with Streamlit
A decorator is a Python construct that modifies or extends a function or class by wrapping it with additional behavior.
- How it is used
- Applies caching and popup-dialog behavior to Streamlit functions without rewriting their core data-loading or rendering logic.
- How deep it goes
- Defines decorators through two working Streamlit examples, but does not explain decorator implementation internals.
- Examples
- Uses @st.cache_data on load_data and @st.dialog on a drilldown function displaying main and comparison dataframes.
- What you can do after
- Apply Streamlit decorators to cache data-loading results and render interactive drilldown content in modal dialogs.
Read how Build Python Web Apps with Streamlit explains decorator →
Pro Angular 16
A decorator is a language construct that attaches metadata or behavior to a class or other declaration.
- How it is used
- Identifies an Angular class as a component and configures how its generated content enters the page.
- How deep it goes
- Defines metadata properties and traces selector matching to a custom element, while deferring further runtime details.
- Examples
- Uses AppComponent with app-root, app.component.html, and app.component.css in a todo application.
- What you can do after
- Apply it via Angular to configure a component class and connect it to an HTML element.
Related concepts
- injectable decoratorincludes · The Injectable decorator is an Angular class decorator that marks a class as eligible for dependency injection and configures its injectable metadata.
- component decoratorincludes · A component decorator is an annotation or decorator that attaches metadata to a class or other program element to identify or configure it as a framework component.
- functionuses · A function is a callable program unit that performs an operation, may accept inputs, and can produce a result or side effect.
- ClassMethodDecoratorContextuses · ClassMethodDecoratorContext is a TypeScript decorator context type that describes the context supplied to a class method decorator, including its class type and method signature.
- with statementalternative to · A with statement is Python syntax that executes a block under a context manager’s control and invokes its entry and exit behavior.
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