Espruino in power converter applications

That's great! Some quick ideas:

• Try using a 'normal' array and use data.push(...) to append, rather than referencing individual elements (this may be faster but I'm not 100% sure)
  
• Define data locally as a single character variable name (d)
  
• Count down towards zero (which will marginally speed up the loop)
  
• Don't do the subtraction of time in the main loop
  
  

Something like this might be faster:

function read() {
  var t=getTime();
  var d = [];
  for (var i=samples; i>0;i--) d.push([getTime(),analogRead(C1),analogRead(C5)]);
  for (i in d) d[i][0]-=t;
  return d;
}
...
var data = capture();

It's all a bit nasty though. I'm actually working on a Waveform class which will allow you to capture and play back analog values. Initial tests look like it'll be able to do it at ~100kHz.