（函数fn（）{…}）（）不起作用

Question

I'm trying to incorporate some crazy callback-recursion combo into my Node.js app. After some research, I found a strange syntax to both declare and execute function in the same block. So I try this simple code to test the concept:

 (function hello() { console.log("Hello, world!"); })(); hello(); 

I expect it to just put two Hello, world! 's in the console. One immediately after declaration and one for the hello() call. However, it just prints one and then throws an error saying hello is not defined at hello() .

Is there something I'm not getting here?

Answer 1

A named function expression only creates a variable with the same name as itself within its own scope. This is useful if you need to call it recursively.

(function hello() {
    // "hello" exists as a variable only here, inside the function
    console.log("Hello, world!");
})();

You need a function declaration to create a matching variable in the same scope as the function is declared (and you can't immediately invoke a function declaration).

 function hello() { console.log("Hello, world!"); } hello(); hello();