systemjs/dist/s.js

Dynamic ES module loader

/*
* SJS 4.0.1
* Minimal SystemJS Build
*/
(function () {
  const hasSelf = typeof self !== 'undefined';

  const envGlobal = hasSelf ? self : global;

  let baseUrl;

  if (typeof document !== 'undefined') {
    const baseEl = document.querySelector('base[href]');
    if (baseEl)
      baseUrl = baseEl.href;
  }

  if (!baseUrl && typeof location !== 'undefined') {
    baseUrl = location.href.split('#')[0].split('?')[0];
    const lastSepIndex = baseUrl.lastIndexOf('/');
    if (lastSepIndex !== -1)
      baseUrl = baseUrl.slice(0, lastSepIndex + 1);
  }

  const backslashRegEx = /\\/g;
  function resolveIfNotPlainOrUrl (relUrl, parentUrl) {
    if (relUrl.indexOf('\\') !== -1)
      relUrl = relUrl.replace(backslashRegEx, '/');
    // protocol-relative
    if (relUrl[0] === '/' && relUrl[1] === '/') {
      return parentUrl.slice(0, parentUrl.indexOf(':') + 1) + relUrl;
    }
    // relative-url
    else if (relUrl[0] === '.' && (relUrl[1] === '/' || relUrl[1] === '.' && (relUrl[2] === '/' || relUrl.length === 2 && (relUrl += '/')) ||
        relUrl.length === 1  && (relUrl += '/')) ||
        relUrl[0] === '/') {
      const parentProtocol = parentUrl.slice(0, parentUrl.indexOf(':') + 1);
      // Disabled, but these cases will give inconsistent results for deep backtracking
      //if (parentUrl[parentProtocol.length] !== '/')
      //  throw Error('Cannot resolve');
      // read pathname from parent URL
      // pathname taken to be part after leading "/"
      let pathname;
      if (parentUrl[parentProtocol.length + 1] === '/') {
        // resolving to a :// so we need to read out the auth and host
        if (parentProtocol !== 'file:') {
          pathname = parentUrl.slice(parentProtocol.length + 2);
          pathname = pathname.slice(pathname.indexOf('/') + 1);
        }
        else {
          pathname = parentUrl.slice(8);
        }
      }
      else {
        // resolving to :/ so pathname is the /... part
        pathname = parentUrl.slice(parentProtocol.length + (parentUrl[parentProtocol.length] === '/'));
      }

      if (relUrl[0] === '/')
        return parentUrl.slice(0, parentUrl.length - pathname.length - 1) + relUrl;

      // join together and split for removal of .. and . segments
      // looping the string instead of anything fancy for perf reasons
      // '../../../../../z' resolved to 'x/y' is just 'z'
      const segmented = pathname.slice(0, pathname.lastIndexOf('/') + 1) + relUrl;

      const output = [];
      let segmentIndex = -1;
      for (let i = 0; i < segmented.length; i++) {
        // busy reading a segment - only terminate on '/'
        if (segmentIndex !== -1) {
          if (segmented[i] === '/') {
            output.push(segmented.slice(segmentIndex, i + 1));
            segmentIndex = -1;
          }
        }

        // new segment - check if it is relative
        else if (segmented[i] === '.') {
          // ../ segment
          if (segmented[i + 1] === '.' && (segmented[i + 2] === '/' || i + 2 === segmented.length)) {
            output.pop();
            i += 2;
          }
          // ./ segment
          else if (segmented[i + 1] === '/' || i + 1 === segmented.length) {
            i += 1;
          }
          else {
            // the start of a new segment as below
            segmentIndex = i;
          }
        }
        // it is the start of a new segment
        else {
          segmentIndex = i;
        }
      }
      // finish reading out the last segment
      if (segmentIndex !== -1)
        output.push(segmented.slice(segmentIndex));
      return parentUrl.slice(0, parentUrl.length - pathname.length) + output.join('');
    }
  }

  /*
   * SystemJS Core
   * 
   * Provides
   * - System.import
   * - System.register support for
   *     live bindings, function hoisting through circular references,
   *     reexports, dynamic import, import.meta.url, top-level await
   * - System.getRegister to get the registration
   * - Symbol.toStringTag support in Module objects
   * - Hookable System.createContext to customize import.meta
   * - System.onload(id, err?) handler for tracing / hot-reloading
   * 
   * Core comes with no System.prototype.resolve or
   * System.prototype.instantiate implementations
   */

  const hasSymbol = typeof Symbol !== 'undefined';
  const toStringTag = hasSymbol && Symbol.toStringTag;
  const REGISTRY = hasSymbol ? Symbol() : '@';

  function SystemJS () {
    this[REGISTRY] = {};
  }

  const systemJSPrototype = SystemJS.prototype;
  systemJSPrototype.import = function (id, parentUrl) {
    const loader = this;
    return Promise.resolve(loader.resolve(id, parentUrl))
    .then(function (id) {
      const load = getOrCreateLoad(loader, id);
      return load.C || topLevelLoad(loader, load);
    });
  };

  // Hookable createContext function -> allowing eg custom import meta
  systemJSPrototype.createContext = function (parentId) {
    return {
      url: parentId
    };
  };

  let lastRegister;
  systemJSPrototype.register = function (deps, declare) {
    lastRegister = [deps, declare];
  };

  /*
   * getRegister provides the last anonymous System.register call
   */
  systemJSPrototype.getRegister = function () {
    const _lastRegister = lastRegister;
    lastRegister = undefined;
    return _lastRegister;
  };

  function getOrCreateLoad (loader, id, firstParentUrl) {
    let load = loader[REGISTRY][id];
    if (load)
      return load;

    const importerSetters = [];
    const ns = Object.create(null);
    if (toStringTag)
      Object.defineProperty(ns, toStringTag, { value: 'Module' });
    
    let instantiatePromise = Promise.resolve()
    .then(function () {
      return loader.instantiate(id, firstParentUrl);
    })
    .then(function (registration) {
      if (!registration)
        throw Error('Module ' + id + ' did not instantiate');
      function _export (name, value) {
        // note if we have hoisted exports (including reexports)
        load.h = true;
        let changed = false;
        if (typeof name !== 'object') {
          if (!(name in ns) || ns[name] !== value) {
            ns[name] = value;
            changed = true;
          }
        }
        else {
          for (let p in name) {
            let value = name[p];
            if (!(p in ns) || ns[p] !== value) {
              ns[p] = value;
              changed = true;
            }
          }
        }
        if (changed)
          for (let i = 0; i < importerSetters.length; i++)
            importerSetters[i](ns);
        return value;
      }
      const declared = registration[1](_export, registration[1].length === 2 ? {
        import: function (importId) {
          return loader.import(importId, id);
        },
        meta: loader.createContext(id)
      } : undefined);
      load.e = declared.execute || function () {};
      return [registration[0], declared.setters || []];
    });

    const linkPromise = instantiatePromise
    .then(function (instantiation) {
      return Promise.all(instantiation[0].map(function (dep, i) {
        const setter = instantiation[1][i];
        return Promise.resolve(loader.resolve(dep, id))
        .then(function (depId) {
          const depLoad = getOrCreateLoad(loader, depId, id);
          // depLoad.I may be undefined for already-evaluated
          return Promise.resolve(depLoad.I)
          .then(function () {
            if (setter) {
              depLoad.i.push(setter);
              // only run early setters when there are hoisted exports of that module
              // the timing works here as pending hoisted export calls will trigger through importerSetters
              if (depLoad.h || !depLoad.I)
                setter(depLoad.n);
            }
            return depLoad;
          });
        })
      }))
      .then(function (depLoads) {
        load.d = depLoads;
      });
    });

    linkPromise.catch(function (err) {
      load.e = null;
      load.er = err;
    });

    // Captial letter = a promise function
    return load = loader[REGISTRY][id] = {
      id: id,
      // importerSetters, the setters functions registered to this dependency
      // we retain this to add more later
      i: importerSetters,
      // module namespace object
      n: ns,

      // instantiate
      I: instantiatePromise,
      // link
      L: linkPromise,
      // whether it has hoisted exports
      h: false,

      // On instantiate completion we have populated:
      // dependency load records
      d: undefined,
      // execution function
      // set to NULL immediately after execution (or on any failure) to indicate execution has happened
      // in such a case, pC should be used, and pLo, pLi will be emptied
      e: undefined,

      // On execution we have populated:
      // the execution error if any
      er: undefined,
      // in the case of TLA, the execution promise
      E: undefined,

      // On execution, pLi, pLo, e cleared

      // Promise for top-level completion
      C: undefined
    };
  }

  function instantiateAll (loader, load, loaded) {
    if (!loaded[load.id]) {
      loaded[load.id] = true;
      // load.L may be undefined for already-instantiated
      return Promise.resolve(load.L)
      .then(function () {
        return Promise.all(load.d.map(function (dep) {
          return instantiateAll(loader, dep, loaded);
        }));
      })
    }
  }

  function topLevelLoad (loader, load) {
    return load.C = instantiateAll(loader, load, {})
    .then(function () {
      return postOrderExec(loader, load, {});
    })
    .then(function () {
      return load.n;
    });
  }

  // the closest we can get to call(undefined)
  const nullContext = Object.freeze(Object.create(null));

  // returns a promise if and only if a top-level await subgraph
  // throws on sync errors
  function postOrderExec (loader, load, seen) {
    if (seen[load.id])
      return;
    seen[load.id] = true;

    if (!load.e) {
      if (load.er)
        throw load.er;
      if (load.E)
        return load.E;
      return;
    }

    // deps execute first, unless circular
    let depLoadPromises;
    load.d.forEach(function (depLoad) {
      {
        const depLoadPromise = postOrderExec(loader, depLoad, seen);
        if (depLoadPromise)
          (depLoadPromises = depLoadPromises || []).push(depLoadPromise);
      }
    });
    if (depLoadPromises) {
      return Promise.all(depLoadPromises).then(doExec);
    }

    return doExec();

    function doExec () {
      try {
        let execPromise = load.e.call(nullContext);
        if (execPromise) {
          execPromise = execPromise.then(function () {
              load.C = load.n;
              load.E = null;
            });
          return load.E = load.E || execPromise;
        }
        // (should be a promise, but a minify optimization to leave out Promise.resolve)
        load.C = load.n;
      }
      catch (err) {
        load.er = err;
        throw err;
      }
      finally {
        load.L = load.I = undefined;
        load.e = null;
      }
    }
  }

  envGlobal.System = new SystemJS();

  /*
   * Supports loading System.register via script tag injection
   */

  const systemRegister = systemJSPrototype.register;
  systemJSPrototype.register = function (deps, declare) {
    err = undefined;
    systemRegister.call(this, deps, declare);
  };

  systemJSPrototype.instantiate = function (url, firstParentUrl) {
    const loader = this;
    if (url.substr(-5) === '.json') {
      return fetch(url).then(function (resp) {
        return resp.text();
      }).then(function (source) {
        return [[], function(_export) {
          return {execute: function() {_export('default', JSON.parse(source));}};
        }];
      });
    } else {
      return new Promise(function (resolve, reject) {
        let err;

        function windowErrorListener(evt) {
          if (evt.filename === url)
            err = evt.error;
        }

        window.addEventListener('error', windowErrorListener);

        const script = document.createElement('script');
        script.charset = 'utf-8';
        script.async = true;
        script.crossOrigin = 'anonymous';
        script.addEventListener('error', function () {
          window.removeEventListener('error', windowErrorListener);
          reject(Error('Error loading ' + url + (firstParentUrl ? ' from ' + firstParentUrl : '')));
        });
        script.addEventListener('load', function () {
          window.removeEventListener('error', windowErrorListener);
          document.head.removeChild(script);
          // Note that if an error occurs that isn't caught by this if statement,
          // that getRegister will return null and a "did not instantiate" error will be thrown.
          if (err) {
            reject(err);
          }
          else {
            resolve(loader.getRegister());
          }
        });
        script.src = url;
        document.head.appendChild(script);
      });
    }
  };

  /*
   * Supports loading System.register in workers
   */

  if (hasSelf && typeof importScripts === 'function')
    systemJSPrototype.instantiate = function (url) {
      const loader = this;
      return new Promise(function (resolve, reject) {
        try {
          importScripts(url);
        }
        catch (e) {
          reject(e);
        }
        resolve(loader.getRegister());
      });
    };

  systemJSPrototype.resolve = function (id, parentUrl) {
    const resolved = resolveIfNotPlainOrUrl(id, parentUrl || baseUrl);
    if (!resolved) {
      if (id.indexOf(':') !== -1)
        return Promise.resolve(id);
      throw Error('Cannot resolve "' + id + (parentUrl ? '" from ' + parentUrl : '"'));
    }
    return Promise.resolve(resolved);
  };

}());