Hey there! Let's break this down clearly so you understand exactly what's going on here.

First, Recapping the Function Type #

You already noted this relates to functions with no return value, and you're right: () => void is a TypeScript type that describes an arrow function with no parameters that returns nothing (void means the function doesn't produce a return value, even if it does have side effects like logging to the console).

The Array Syntax Explained #

The [] at the end is what turns this single function type into an array of those functions. The parentheses around () => void are critical here—they group the function type together so the [] applies to the entire function type, not just the return value.

In short:
(() => void)[] = An array where every element is a function that takes no arguments and returns void

Breaking Down Your Examples #

1. Standalone Type & Initialization #

// This declares a variable with a type of "array of void-returning, no-arg functions", initialized to an empty array
const myFunctionArray: (() => void)[] = [];

You can later add valid functions to this array, like:

myFunctionArray.push(() => console.log("I'm a valid function here!"));
myFunctionArray.push(() => { /* A function that does nothing, still fits the type */ });

2. Class Member Declaration #

class MyService {
  // A public class property that's an array of void-returning, no-arg functions, initialized to empty
  public functionName: (() => void)[] = [];

  // Example method to add functions to the array
  registerCallback(callback: () => void) {
    this.functionName.push(callback);
  }

  // Example method to run all functions in the array
  runAllCallbacks() {
    this.functionName.forEach(callback => callback());
  }
}

This is useful for patterns like callback registries—where a class holds a list of functions to execute later (like event handlers).

A Common Pitfall to Avoid #

Watch out for missing parentheses! If you wrote () => void[] instead, that would mean something totally different: it describes a function with no parameters that returns an array of void values (which isn't very useful, but it's important to know the difference the parentheses make).

内容的提问来源于stack exchange，提问作者JS Lover