Dynamically load JavaScript files with callback when finished

load_script_ajax.js

    atm.loadScript = (function () {
        let loadedScripts = [];

        return function (src, callback) {
            if (~loadedScripts.indexOf(src) && callback) {
                callback();
            }

            $.ajax({
                url: src,
                dataType: 'script',
                success: innerCallback,
                async: true,
                error: function () {
                    console.log(error);
                }
            });

            function innerCallback(script) {
                //eval(script);
                loadedScripts.push(src);
                callback();
            }
        };
    })();

load_script_include_header.js

loadScript = (function () {
        let loadedScripts = [];

        return function (src, callback) {
            if (~loadedScripts.indexOf(src) && callback) {
                callback();
            }

            let script = document.createElement('script'),
                loaded;

            script.setAttribute('src', src);

            if (callback) {
                script.onreadystatechange = script.onload = function () {
                    if (!loaded) {
                        callback();
                    }
                    loaded = true;
                    loadedScripts.push(src);
                };
            }

            document.getElementsByTagName('head')[0].appendChild(script);
        };
    })();