in lib/index.ts [155:165]
export function extend(baseDriver: WebDriver, fallbackGracefully = false): ExtendedWebDriver {
var extender = new Extender(baseDriver);
let extendedDriver: ExtendedWebDriver = baseDriver as ExtendedWebDriver;
for (let commandName in commandDefinitions) {
(extendedDriver as any)[commandName] =
(commandDefinitions as any)[commandName].compile(extender, fallbackGracefully);
}
return extendedDriver;
}