Jitter should be relative to the current delay

[mokesmokes]

E.g. in https://github.com/segmentio/backo/blob/master/index.js#L38
perhaps try something like:

if (this.jitter) {
  var rand =  Math.random();
  var deviation = rand * this.jitter * ms; // 0 <= jitter <= 1
  ms = (Math.floor(rand * 10) & 1) == 0  ? ms - deviation : ms + deviation;  // so jitter is uniformly distributed on both sides
}

[travisjeffery]

so you want to randomly subtract sometimes rather than add?

with the old api jitter will almost certainly not between 0 and 1. we usually use something like 200.

[mokesmokes]

The intent is a distribution based around the mean delay value, as a percentage of the delay value.
200ms, for example, may in some cases be long, and in others short. Thus it should grow as the delay grows. See the PR I just submitted (not yet tested.... will be later today or tomorrow... but for the discussion pushed it)