Decorators
Problem
> ES7 proposal > > The ES7 proposal for decorators can be found here: https://github.com/wycats/javascript-decorators > The ES7 proposal serves as the base of this proposal. Below are notes about how the type system Decorator targets: Class constructor [code block] desugars to: [code block] Methods [code block] desugars to: [code block] Static method [code block] desugars to: [code block] Properties [code block] desugars to: [code block] Method/Accessor formal parameter [code block] desugars to: [code block] Where the __decorate is defined as: [code block] Decorator signatures: A valid decorator should be: 1. Assignable to one of the Decorator types (ClassDecorator | PropertyDecorator | MethodDecorator | ParameterDecorator) as described below. 2. Return a value (in the case of class decorators and method decorator) that is assignable to the decorated value. [code block] Notes: - Decorating a function declaration is not allowed as it will block hoisting the function to the top of the scope, which is a significant change in semantics. - Decorating function expressions and arrow functions are not supported. The same effect can be achived by applying the decorator function as `var x = dec(function () { });` - Decorating function formal parameters is currently not part of the ES7 proposal. - Decorators are not allowed when targeting ES3
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1 Fix
Implement ES7 Decorator Proposal Compliance
The current implementation does not support decorators as specified in the ES7 proposal, leading to issues when attempting to apply decorators to class constructors, methods, and properties. This is primarily due to the lack of support for certain types of decorators and the restrictions on decorating function declarations and expressions.
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- 1
Update TypeScript Compiler Configuration
Ensure that the TypeScript compiler is configured to support the latest ES features, including decorators. Update the tsconfig.json file to include 'experimentalDecorators' and 'emitDecoratorMetadata'.
json```json { "compilerOptions": { "target": "ESNext", "experimentalDecorators": true, "emitDecoratorMetadata": true } } ``` - 2
Refactor Decorator Functions
Ensure that all decorator functions conform to the expected signatures. Class decorators should return a class, method decorators should return a method, and property decorators should return a property descriptor.
typescript```typescript function MyDecorator(target: any, propertyKey: string, descriptor: PropertyDescriptor) { // Modify the method or property descriptor return descriptor; } ``` - 3
Remove Unsupported Decorator Usages
Identify and remove any usages of decorators on function declarations and expressions, as these are not supported. Instead, apply decorators to class methods and properties only.
typescript```typescript class MyClass { @MyDecorator myMethod() { // method implementation } } ``` - 4
Test Decorator Functionality
Create unit tests to verify that decorators are functioning as intended. Ensure that class decorators, method decorators, and property decorators are correctly modifying the target entities.
typescript```typescript describe('MyDecorator', () => { it('should modify the method', () => { const instance = new MyClass(); // Assert that the method behavior is as expected }); }); ``` - 5
Document Changes and Usage
Update documentation to reflect the changes made to the decorator implementation and provide examples of correct usage according to the ES7 proposal.
Validation
Confirm that the TypeScript compiler compiles without errors and that all unit tests pass. Additionally, verify that decorators are functioning correctly in the application by checking the behavior of decorated classes and methods.
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Environment
Submitted by
Alex Chen
2450 rep