从点击侦听器调用公共方法时，为什么需要匿名函数来封装

Question

I have a decent feel for scope and execution flow, but I'm having trouble grasping why this doesn't work:

var modalWindow = (function() {
    // Other code...
    modalBtn.addEventListener('click', modalWindow.closeModal);
    return {
        closeModal: function() {
            modalContainer.remove();
        }
    }
}());

And this does:

var modalWindow = (function() {
    // Other code...
    modalBtn.addEventListener('click', function() {
        modalWindow.closeModel());
    });
    return {
        closeModal: function() {
            modalContainer.remove();
        }
    }
}());

The first throws modalWindow is undefined. I know I could just declare a named object and place closeModal in it, then reference it, and I wouldn't need the anonymous function in the listener. But I'm curious as to why the latter works as is.

Answer 1

The code you provided has an unmatched ( .

I'm betting the end really looks something like:

})();

The value of modalWindow is the return value of the IIFE … but it doesn't get that value until the IIFE has finished executing and actually returned a value.

Until then, the value is undefined so when you try to read it before the IIFE is finished, it errors.