Expert Angular

Parameter decorators

Parameter decorators are prefixed to parameter declarations, and they are applied to a function for a class constructor or a method declaration. The signature of ParameterDecorator is as follows:

declare type ParameterDecorator = (target: Object, propertyKey:  
   string | symbol, parameterIndex: number) => void; 

Now, let's define the Customer class and use a parameter decorator to decorate a parameter in order to make it required and validate whether the value has been served:

class Customer { 
    constructor() {  } 
  
    getName(@logging name: string) { 
        return name; 
   } 
} 

Here, the name parameter has been decorated with @logging. The parameter decorator implicitly takes three inputs, namely prototype of the class that has this decorator, ...