module-types.js

/*
 * Loads JSON, CSS, Wasm module types based on file extensions
 * Supports application/javascript falling back to JS eval
 */
(function(global) {
  const systemJSPrototype = global.System.constructor.prototype;
  const instantiate = systemJSPrototype.instantiate;

  systemJSPrototype.instantiate = function (url, parent) {
    const loader = this;
    const ext = url.slice(url.lastIndexOf('.'));
    switch (ext) {
      case '.css':
        return loadDynamicModule(function (_export, source) {
          // Relies on a Constructable Stylesheet polyfill
          const stylesheet = new CSSStyleSheet();
          stylesheet.replaceSync(source);
          _export('default', stylesheet);
        });
      case '.html':
        return getSourceRes().then(function (res) {
          return maybeJSFallback(res) || loadError("'.html' modules not implemented");
        });
      case '.json':
        return loadDynamicModule(function (_export, source) {
          _export('default', JSON.parse(source));
        });
      case '.wasm':
        return getSourceRes().then(function (res) {
          return maybeJSFallback(res) ||
              (WebAssembly.compileStreaming ? WebAssembly.compileStreaming(res) : res.arrayBuffer().then(WebAssembly.compile));
        })
        .then(function (module) {
          const deps = [];
          const setters = [];
          const importObj = {};
      
          // we can only set imports if supported (eg early Safari doesnt support)
          if (WebAssembly.Module.imports)
            WebAssembly.Module.imports(module).forEach(function (impt) {
              const key = impt.module;
              if (deps.indexOf(key) === -1) {
                deps.push(key);
                setters.push(function (m) {
                  importObj[key] = m;
                });
              }
            });
      
          return [deps, function (_export) {
            return {
              setters: setters,
              execute: function () {
                return WebAssembly.instantiate(module, importObj)
                .then(function (instance) {
                  _export(instance.exports);
                });
              }
            };
          }];
        });
    }
    return instantiate.apply(this, arguments);

    function getSourceRes () {
      return fetch(url).then(function (res) {
        if (!res.ok)
          loadError(res.status + ' ' + res.statusText);
        return res;
      });
    }
    function maybeJSFallback (res) {
      const contentType = res.headers.get('content-type');
      // if the resource is sent as application/javascript, support eval-based execution
      if (contentType && contentType.match(/^application\/javascript(;|$)/)) {
        return res.text().then(function (source) {
          (0, eval)(source);
          return loader.getRegister();
        });
      }
    }
    function loadDynamicModule (createExec) {
      return getSourceRes().then(function (res) {
        return maybeJSFallback(res) || res.text().then(function (source) {
          return [[], function (_export) {
            return { execute: createExec(_export, source) };
          }];
        });
      });
    }
    function loadError (msg) {
      throw Error(msg + ', loading ' + url + (parent ? ' from ' + parent : ''));
    }
  };
})(typeof self !== 'undefined' ? self : global);