code: function onClientPreRequestCircuitBreaker (ctx, next) {
    if (ctx._config.circuitBreaker.enabled) {
      // any pattern represent an own circuit breaker
      const circuitBreaker = ctx._circuitBreakerMap.get(ctx.trace$.method);
      if (!circuitBreaker) {
        const cb = new CircuitBreaker(ctx._config.circuitBreaker);
        ctx._circuitBreakerMap.set(ctx.trace$.method, cb);
      } else {
        if (!circuitBreaker.available()) {
          // trigger half-open timer
          circuitBreaker.record();
          return next(new Errors.CircuitBreakerError(
            `Circuit breaker is ${circuitBreaker.state}`,
            { state: circuitBreaker.state, method: ctx.trace$.method, service: ctx.trace$.service }));
        }
      }
  
      next();
    } else {
      next();
    }
  }
docs: circuit breaker on client side