We present ContextAmber, a framework for context-oriented programming, in Amber Smalltalk, an implementation of the Smalltalk programming language that compiles to JavaScript. ContextAmber is implemented using metaprogramming facilities and supports global, object-wise, and scoped layer activation. Current COP implementations come at the expense of significantly reduced execution performance due to multiple partial method invocations and layer composition computations every time a layered method is invoked. ContextAmber can reduce this overhead by inlining partial methods, caching layer compositions, and caching inlined layered methods, resulting in a runtime overhead of about 5% in our vector graphics rendering benchmarks.