我如何理解这段 JavaScript 代码的含义？

Question

What does this JavaScript code mean?

img.file = file;

const reader = new FileReader();
reader.onload = (function(aImg) { 
    return function(e) { 
        aImg.src = e.target.result; 
    }; 
})(img);

Specifically this

reader.onload = (function(){...})()

Answer 1

This is an Immediately Invoked Function Expression (IIFE)

https://developer.mozilla.org/en-US/docs/Glossary/IIFE would be helpful in your case.

It creates a function and immediately calls it. You can find some use cases in the link above