JSFiddle - React, Tailwind, and code Playground

JavaScript

var loaded = 0;

for(var i = 0; i < 10; i++){
    for(var j = 0; j < 10;j++){
        var img = new Image();
        img.onload = (function (i,j,img) {
            console.log(loaded);
            return function () {
                loaded++;
                if(loaded == 20) callback();
            };
        }(i,j,img));        
    };
};

function callback(){
 alert();   
}