lib/strategy/exponential.js
function ExponentialBackoffStrategy(options) {
    BackoffStrategy.call(this, options);
    this.backoffDelay_ = 0;
    this.nextBackoffDelay_ = this.getInitialDelay();
    this.factor_ = ExponentialBackoffStrategy.DEFAULT_FACTOR;

    if (options && options.factor !== undefined) {
        precond.checkArgument(options.factor > 1,
            'Exponential factor should be greater than 1 but got %s.',
            options.factor);
        this.factor_ = options.factor;
    }
}
function ExponentialBackoffStrategy(options) {
    BackoffStrategy.call(this, options);
    this.backoffDelay_ = 0;
    this.nextBackoffDelay_ = this.getInitialDelay();
    this.factor_ = ExponentialBackoffStrategy.DEFAULT_FACTOR;

    if (options && options.factor !== undefined) {
        precond.checkArgument(options.factor > 1,
            'Exponential factor should be greater than 1 but got %s.',
            options.factor);
        this.factor_ = options.factor;
    }
}
Exponential backoff strategy.