Issues with identifying the signature of a class decorator arise when invoked as an expression

I've been following this coding example but I'm running into issues when trying to compile it. Any suggestions on how to troubleshoot this error?

import { Component } from '@angular/core';

function log(className)
{
  console.log(className)

  return (...args) => {
    console.log("Arguments passed to this class's constructor are ", args)
    return new className(...args)
  }
}

@log
class myExampleClass
{
    constructor(arg1, arg2)
    {
      console.log("Constructor fired!")
    }
}

const myClass = new myExampleClass(5,10)

The specific error message I'm receiving states:

Unable to resolve signature of class decorator when called as an expression.
  Type '(...args: any[]) => any' is not assignable to type 'typeof myExampleClass'.
    Type '(...args: any[]) => any' provides no match for the signature 'new (arg1: any, arg2: any): myExampleClass'.

Answer №1

The decorator for classes is added to the constructor of the class and has the ability to observe, modify, or substitute a class definition.

In this scenario, you are attempting to substitute a class definition. In such cases, it is necessary to return the same type as the class to which your @log decorator is applied.

function log<T extends { new(...args: any[]): {} }>(className: T) {
  console.log(className)
  return class extends className {
    constructor(...args) {
      super(...args);
      console.log("Arguments provided to the constructor of this class are ", args)
    }
  }
} 

For further information, refer to:

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