load scripts

var _loadScript = function(path){
    var script= document.createElement('script');
    script.type= 'text/javascript';
    script.src= path;
    document.head.appendChild(script);
};

function fetchLocal(url) {
  return new Promise(function(resolve, reject) {
    var xhr = new XMLHttpRequest
    xhr.onload = function() {
      resolve(new Response(xhr.responseText, {status: xhr.status}))
    }
    xhr.onerror = function() {
      reject(new TypeError('Local request failed'))
    }
    xhr.open('GET', url)
    xhr.send(null)
  })
}

fetchLocal('url/lib.js')
    .then(response => response.text())
    .then(text => eval(text))
    .then(() => { /* now you can use your library */ })


//document.write, goog.require etc

var CLOSURE_DEFINES = {'goog.ENABLE_CHROME_APP_SAFE_SCRIPT_LOADING': true};
document.write('<script src="url/lib.js"></script>');
goog.require("foo.core")