Load remote JavaScript files programatically at runtime

loader.js

//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// 
// Allows you to load JavaScript files programatically from within other JavaScript files in your project.
//
// Instructions:
// 1. Include this file before all other scripts in your project.
// 2. Call jsLoader.load() or jsLoader.loadAsync() from within your scripts passing a single JS file path or 
// array of multiple JS paths to load into your script at runtime.
// 
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// 
const jsLoader = {
    _toArray: data => (Array.isArray(data) ? data : [data]),
    load: files => {
        files = this._toArray(files);
        
        let script = document.createElement('script');
        script.setAttribute('type', 'text/javascript');
        script.setAttribute('src', files[0]); 
        
        document.getElementsByTagName('head')[0].appendChild(script);
        console.log("%cLoader.js loaded => " + "%c" + files[0], 'background: #222; color: #3BFF00', '');
        
        if(files.length > 1){
           this.load(files.slice(1));
        }    
    },
    loadAsync: files => {
        let loadScript = (file) => {
            return new Promise((resolve, reject) => {
                let xhr = new XMLHttpRequest();
                xhr.onreadystatechange = () => {
                    
                    if(xhr.readyState !== 4) {
                        return;
                    }
                    
                    if(xhr.status === 200) {
                        try {
                            eval(xhr.response);
                            console.log("%cLoader.js xhr loaded => " + "%c" + file, 'background: #222; color: #3BFF00', '');
                            resolve(file);
                            return;
                        }
                        catch(e) {
                            console.log(
                                "%cLoader.js eval failed => " + "%c" + file + "%c. Attempting alternate method.", 
                                'background: #222; color: #FFD400',
                                '',
                                ''
                            );
                        }
                    }

                    let script = document.createElement('script');
                    script.setAttribute('type', 'text/javascript');
                    script.setAttribute('async', 1); 
                    script.setAttribute('src', file); 
                    
                    script.onload = script.onreadystatechange = (args, msg) => {
                        if(msg || !script.readyState || /loaded|complete/.test(script.readyState)) {
                            
                            script.onload = script.onreadystatechange = null;
                            script = null;
         
                            if(!msg) {
                                console.log("%cLoader.js inject loaded => " + "%c" + file, 'background: #222; color: #3BFF00', '');
                                resolve(file);
                            }
                            else {
                                console.error("Loader.js failed => " + "%c" + file, 'background: #222; color: #FF2D00', '');
                                reject(file);
                            }
                        }
                    };
                    document.getElementsByTagName('head')[0].appendChild(script);
                };
                
                xhr.open('GET', file, true);
                xhr.send('');
            });
        }
        
        files = this._toArray(files);
        
        return new Promise((resolve, reject) => {
            let promises = files.map(x => loadScript(x));
            return Promise.all(promises).then(files => resolve(files), files => reject(files));
        });
    }
};