has(name) {
    if (this.namespace.has(name)) { return true; }
    if (this.reexports.has(name)) { return true; }

    // default exports must be explicitly re-exported (#328)
    if (name !== 'default') {
      for (const dep of this.dependencies) {
        const innerMap = dep();

        // todo: report as unresolved?
        if (!innerMap) { continue; }

        if (innerMap.has(name)) { return true; }
      }
    }

    return false;
  }
Note that this does not check explicitly re-exported names for existence
in the base namespace, but it will expand all `export * from '...'` exports
if not found in the explicit namespace.
@param  {string}  name
@return {boolean} true if `name` is exported by this module.