React useCallback回调函数参数来源及示例解析

Hey there! Let's break down your questions about useCallback clearly and simply.

1. Where do the parameters inside the useCallback callback come from? #

Great question! The parameters inside the callback wrapped by useCallback don’t come from useCallback itself or its dependency array. Instead, they’re passed in when you actually call that cached callback function somewhere in your component code.

Think of useCallback as just a memoization tool—it keeps your callback from being recreated on every render unless its dependencies change. The callback’s own parameters are 100% determined by how and where you invoke it later. For example:

const handleClick = useCallback((event) => {
  // The `event` here is what we pass when calling handleClick
  console.log(event.target.value);
}, []);

// Later in your component...
<button onClick={(e) => handleClick(e)}>Click Me</button>

Here, the event parameter inside the useCallback callback is the click event object we passed from the button’s onClick handler.

2. Breaking down your useMenu example #

Let’s walk through your specific code snippet:

export const useMenu = (id1, id2, id3) => useCallback(({row, column, id}, myProps) => { 
  doSomething(); 
}, [id1, id2, id3]);

// Usage in a component
const myMenu = useMenu(123, 345, 567);

Here’s exactly where each parameter comes from:

• row, column, and id: These are properties of the first argument you pass when calling myMenu. For example, if you write:

  myMenu({ row: "user-row-1", column: "action-col", id: 789 }, { isAdmin: true });
  

  Inside the callback, row will be "user-row-1", column will be "action-col", and id will be 789. This object is entirely defined when you invoke myMenu, not by the id1/id2/id3 inputs or the useCallback dependency array.
• myProps: This is the second argument you pass when calling myMenu. In the example above, it would be the object { isAdmin: true }—again, determined entirely by how you call the function later.

A quick reminder: The [id1, id2, id3] dependency array only controls when useCallback creates a new version of the callback function (it updates when any of these IDs change). It has no impact on the parameters that get passed into the callback when you call it.

内容的提问来源于stack exchange，提问作者Neel Dsouza