Each method in a class can also have its own decorators.

> Similar to property decorators, parameter decorators are generally not used alone, but are used in combination with class or method decorators.

## Parameters

1.  *target* is the constructor of the class for static members, and the prototype object of the class for instance members.

2.  *key* method name

3.  *index* position in the parameter array

For example, if we need to format the parameters of a method, we can create a decorator specifically for formatting.

```typescript
// Parameter formatting configuration
const parseConf: ((...args: any[]) => any)[] = [];

export const parse =
    (parseTo: (...args: any[]) => any) =>
    (target: any, propertyName: string, index: number) => {
        parseConf[index] = parseTo;
    };

// Perform formatting operations before function call.
export const parseDecorator = (
    target: any,
    propertyName: string,
    descriptor: PropertyDescriptor,
): PropertyDescriptor => {
    console.log('Start formatting data.');
    return {
        ...descriptor,
        value(...args: any[]) {
            // Get the formatted parameter list.
            const newArgs = args.map((v, i) =>
                parseConf[i] ? parseConf[i](v) : v,
            );
            console.log('Finished formatting data.');
            return descriptor.value.apply(this, newArgs);
        },
    };
};

export interface UserType {
    id: number;
    username: string;
}

class UserService {
    private users: UserType[] = [
        { id: 1, username: 'admin' },
        { id: 2, username: 'brian' },
    ];

    getUsers() {
        return this.users;
    }

    @parseDecorator
    delete(@parse((arg: any) => Number(arg)) id: number) {
        this.users = this.users.filter((userObj) => userObj.id !== id);
        return this;
    }
}

export const exp78 = () => {
    console.log();
    console.log(
        '-----------------------Parameter decorator--------------------',
    );
    console.log('---------------Formatting parameters-----------------');
    console.log();
    const userService = new UserService();
    userService.delete(1);
    console.log(userService.getUsers());
    console.log();
    console.log('---------------End-----------------------');
};


// console: [ { id: 2, username: 'brian' } ]
```


5. Parameter Decorator

Each method in a class can also have its own decorators.

> Similar to property decorators,...