code: function tryFinishRequire() {
              if ( !isCallbackCalled ) {
                  var isAllCompleted = 1;
                  each( ids, function ( id ) {
                      if ( !BUILDIN_MODULE[ id ] ) {
                          return ( isAllCompleted = modIsCompleted( id ) );
                      }
                  });
  
                  // 检测并调用callback
                  if ( isAllCompleted ) {
                      isCallbackCalled = 1;
  
                      (typeof callback === 'function') && callback.apply(
                          global,
                          modGetModulesExports( ids, BUILDIN_MODULE )
                      );
                  }
              }
          }
docs: 尝试完成require，调用callback
  在模块与其依赖模块都加载完时调用
  
  @ignore