systemjs/dist/extras/global.js

Dynamic ES module loader

/*
 * SystemJS global script loading support
 * Extra for the s.js build only
 * (Included by default in system.js build)
 */
(function (global) {

const systemJSPrototype = System.constructor.prototype;

// safari unpredictably lists some new globals first or second in object order
let firstGlobalProp, secondGlobalProp, lastGlobalProp;
function getGlobalProp () {
  let cnt = 0;
  let lastProp;
  for (let p in global) {
    if (!global.hasOwnProperty(p))
      continue;
    if (cnt === 0 && p !== firstGlobalProp || cnt === 1 && p !== secondGlobalProp)
      return p;
    cnt++;
    lastProp = p;
  }
  if (lastProp !== lastGlobalProp)
    return lastProp;
}

function noteGlobalProps () {
  // alternatively Object.keys(global).pop()
  // but this may be faster (pending benchmarks)
  firstGlobalProp = secondGlobalProp = undefined;
  for (let p in global) {
    if (!global.hasOwnProperty(p))
      continue;
    if (!firstGlobalProp)
      firstGlobalProp = p;
    else if (!secondGlobalProp)
      secondGlobalProp = p;
    lastGlobalProp = p;
  }
  return lastGlobalProp;
}

const impt = systemJSPrototype.import;
systemJSPrototype.import = function (id, parentUrl) {
  noteGlobalProps();
  return impt.call(this, id, parentUrl);
};

const emptyInstantiation = [[], function () { return {} }];

const getRegister = systemJSPrototype.getRegister;
systemJSPrototype.getRegister = function () {
  const lastRegister = getRegister.call(this);
  if (lastRegister)
    return lastRegister;
  
  // no registration -> attempt a global detection as difference from snapshot
  // when multiple globals, we take the global value to be the last defined new global object property
  // for performance, this will not support multi-version / global collisions as previous SystemJS versions did
  // note in Edge, deleting and re-adding a global does not change its ordering
  const globalProp = getGlobalProp();
  if (!globalProp)
    return emptyInstantiation;
  
  let globalExport;
  try {
    globalExport = global[globalProp];
  }
  catch (e) {
    return emptyInstantiation;
  }

  return [[], function (_export) {
    return {
      execute: function () {
        _export({ default: globalExport, __useDefault: true });
      }
    };
  }];
};

})(typeof self !== 'undefined' ? self : global);