if (!fallbackWorkerSrc && typeof document !== 'undefined') {
var pdfjsFilePath = document.currentScript && document.currentScript.src;
if (pdfjsFilePath) {
fallbackWorkerSrc = pdfjsFilePath.replace(/(.(?:min.)?js)(?.*)?$/i, '.worker$1$2');
}
}
Sometimes “document.currentScript” === null, pdfjsFilePath === null,

function getWorkerSrc() {
if (_worker_options.GlobalWorkerOptions.workerSrc) {
return _worker_options.GlobalWorkerOptions.workerSrc;
}
if (typeof fallbackWorkerSrc !== 'undefined') {
return fallbackWorkerSrc;
}
throw new Error('No "GlobalWorkerOptions.workerSrc" specified.');
}