code: function tryFinishRequire() {
              if (typeof callback === 'function' && !isCallbackCalled) {
                  var isAllCompleted = 1;
                  each(ids, function (id) {
                      if (!BUILDIN_MODULE[id]) {
                          return (isAllCompleted = !!modIs(id, MODULE_DEFINED));
                      }
                  });
  
                  // 检测并调用callback
                  if (isAllCompleted) {
                      isCallbackCalled = 1;
  
                      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
  
  @inner