Fibonacci backoff for promises. Retries a function indefinitely until it succeeds (Promise resolves).

backoff.js

/**
 * Given a function promiseFunctionToRetry that returns a Promise, repeatedly
 * call the function with a fibonacci backoff until it results in a resolved 
 * Promise.
 * @param {function} promiseFunctionToRetry a function that returns a Promise
 *   that can potentially reject. This may be called multiple times.
 * @param {number?} backoff An optional starting backoff in ms (default 1000)
 * @return {Promise} guaranteed to never reject
 */
var backoff = function(promiseFunctionToRetry, backoff) {
  return new Promise(function(resolve) {
    var currentBackoff = backoff || 1000;
    var backoffStep = currentBackoff;

    var retry = function() {
      promiseFunctionToRetry()
          .then(resolve, function() {
            setTimeout(retry, currentBackoff);
            var temp = currentBackoff;
            currentBackoff += backoffStep;
            backoffStep = temp;
          });
    };

    retry();
  });
};