IIFE Inside Loop

Question

I tried hard to understand the code inside for loop, but i couldn't achieve anything. This program outputs A-Z (As an exercise)

Question:

1. Why is there an IIFE inside that loop. why removing it doesn't work. what's it's role.

2. Oh, Damn it, I have lot's of questions about this loop and why it works. I tried with debugging, but no outcome as a teaching material out of it. Can someone please explain it? Like stacking and so one.

debugger;

(function(global){

function C() {
    console.log("OOPS!");
}

function E(f) {
    console.log("E");
    f();
    var f = F;
}
var A = function() {
    console.log("A");
    B();
};

var C;

function G() {
    console.log("G");
    H();

    function H() {
        console.log("H");
        I();
    }
}
var D = d;
function d() {
    console.log("D");
    E(F);
}

function I() {
    console.log("I");
    J();
    J();
}
var B = function() {
    console.log("B");
    C();
};

var F = function() {
    console.log("F");
    G();
};

obj = {};
var rest = "KLMNOPQRSTUVWXYZ".split("");

for (var i=0; i<rest.length; i++) {
    (function(i){
        // define the current function
        obj[rest[i]] = function() {
            console.log(rest[i]);
            if (i < (rest.length-1)) {
                obj[rest[i+1]]();
            }
        };
    })(i);
}

var J = function() {
    J = function() {
        console.log("J");
        obj.K();
    };
};

function C() {
    console.log("C");
    D();
}
return A;
})(window)();