JavaScript bind方法疑问：绑定函数为何无需变量即可触发？

Hey there! Let's unpack this confusion step by step—your core understanding of bind() is totally correct, but the key difference here is who's responsible for calling the bound function.

First, let's recap what bind() does:

• It creates and returns a new copy of your original function where the this context is permanently locked to the object you pass in.
• This new function does need to be called to run—but you don't always have to be the one calling it.

Why .on('keyup', this.create.bind(this)) works without assigning to a variable #

When you pass this.create.bind(this) to the .on() method, you're not executing the function right away. Instead:

1. bind() generates that bound function copy on the fly.
2. The .on() method stores this bound function as an event callback.
3. When the keyup event happens later, the browser's event system automatically calls this stored bound function for you.

Think of it like handing someone a pre-addressed envelope (the bound function) and saying, "Open this when the mail arrives." You don't open it yourself—you let the mail carrier (the event system) do it when the time comes.

Compare this to your console test scenario #

When you test bind() in the console like this:

const boundFn = this.create.bind(this);
boundFn();

You have to call boundFn() manually because there's no event system or other mechanism to trigger it for you. But in the event listener case, the browser takes care of that call when the event fires.

Why no need for call/apply? #

bind() already pre-configures the this context for the function. When the event system calls the bound function, this is already set to the object you passed to bind()—you don't need call or apply to override it again.

Another example to drive this home: if you use setTimeout(this.create.bind(this), 1000), the timer will call the bound function after 1 second, and this will still be your target object—no manual call or call/apply required.

Your initial understanding was spot-on—bind() returns a function that needs execution. The missing piece was realizing that other systems (like event listeners or timers) can handle the execution for you when the right condition is met.

内容的提问来源于stack exchange，提问作者Mimi