Method Spy

methodspy.js

// Where native object is something like AudioContext, localStorage, XMLHttpRequest, etc..
var
  nObject = window.someNativeObject,
  originalMethod = nObject.method;

nObject.method = function () {
  // Do other things here, like track arguments
  originalMethod.apply( nObject, arguments );
}

function MockObject () {
  this.nativeObject = window.someNativeObject;
};
MockObject.prototype = {
  method : function () {
    // Do other things here, like track arguments
    this.nativeObject.apply( this.nativeObject, arguments );
  }
};