Parameter decorators are used to add metadata to the parameters of a method in a class. These decorators receive three arguments: the prototype of the class, the name of the method, and the index of the parameter in the method's argument list.

Syntax of a Parameter Decorator:

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In this example, the parameterDecorator is applied to the param1 parameter of the exampleMethod method of the ExampleClass.

Practical Example:

Suppose we want to implement a decorator that validates that a parameter is not null or undefined before the method is executed.

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In this example, the validateParameter decorator ensures that the param passed to the exampleMethod is not null or undefined. If null or undefined is passed, it will throw an error before the method is executed.