We propose a context-oriented programming (COP) language that allows layers to define base methods, while layers can be asynchronously activated and deactivated. Base methods in layers greatly enhances modularity because they extend classes’ interface without modifying the original class definitions. However, calling such a method defined in a layer is tricky as the layer may not be active when the method is called. We tackle this problem by introducing a method lookup mechanism that uses the lexical scope of a method invocation to COP; i.e., besides currently activated layers, the layer where the method invocation is written, as well as layers on which that layer depends, are considered for method lookup. We implemented this mechanism in ServalCJ, a COP language that supports asynchronous layer activation as well as synchronous layer activation.