Controlling a remote control toy

It depends a bit on your controller, but normal RC vehicles (cars/planes/etc) with discrete receivers tend to send out a pretty simple signal - it's basically a bunch of Servo control signals (roughly 1ms-2ms) of varying polarities put end to end...

             _______     __________            __          ___
____________|       |___|          |__________|  |________|   |_________________________
 ....         S1      S2    S3          S4     S5   S6      S7       .....

I'm pretty sure that's what happens anyway (perhaps with more than 7 servo signals though). That's then transmitted over and over, with a large gap between the signals so the receiver can sync up.

You may be able to find a transmitter that'll take that signal (or find a point where you can 'inject' the signal into your existing transmitter - and then it's pretty easy to recreate it with Espruino. To be sure about that you'd want to prod around with an Oscilloscope though.

Having said that. @DrAzzy is probably right - it's a lot simpler to just modify your existing remote control :)