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I use an event dispatcher to register and fire events within classes in TypeScript. The code works fine. For a better code quality I use TSLint, which is unhappy about a the way I declare the handler, but I do not understand the description.

The code fragment:

export type Handler<E> = (event: E) => void;

export class EventDispatcher<E> 
 private handlers: Handler<E> = ;

 public fire(event: E) 
 for (const h of this.handlers) 
 h(event);
 
 

 public register(handler: Handler<E>) 
 this.handlers.push(handler);
 

TSLint is unhappy about line 4 in the code, specifically about Handler<E>. The message is:

[tslint] Array type using 'T' is forbidden for non-simple types. Use
'Array' instead. (array-type) [tslint] Array type using 'T' is
forbidden for non-simple types. Use 'Array' instead. type
Handler = (event: E) => void

I do not fully understand what TSLint wants me to do. Why is T forbidden? What is meant with a non-simple type? It also sais that I should use an array instead, but Handler<E> already is an array. So where is there problem?

Arrays of non-simple types are hard to read. Consider a variable defined as:

let foo: prop1: string; prop2: string;

It might be easy to miss the at the end with such a log item type. Even in your case since the item of the array is a generic type it might be easy to miss the at the end after the <..>.

The linter wants you to use the long form of array, the generic Array<T> type. The two forms are perfectly equivalent, so it's just a readability issue. In your case, this should work

export type Handler<E> = (event: E) => void;

export class EventDispatcher<E> 
 private handlers: Array<Handler<E>> = ;

 public fire(event: E) 
 for (const h of this.handlers) 
 h(event);
 
 

 public register(handler: Handler<E>) 
 this.handlers.push(handler);