Send to server stream for Browser Bunyan

server-stream.js

const userAgent = typeof window !== 'undefined' ? window.navigator.userAgent : 'no-window';
const isBot = /bot|crawler|spider|crawling/i.test(userAgent);

export class ServerLogStream {

    constructor(opts = {}) {
        const {
            writeCondition = ServerLogStream.defaultWriteCondition,
        } = opts;

        this.opts = opts;
        this.writeCondition = writeCondition;
        this.records = {};

        this.start();
    }

    start() {
        const {
            method = 'PUT',
            url = '/log',
            throttleInterval = 3000,
            withCredentials = false,
            onError,
        } = this.opts;

        const throttleRequests = () => {
            // wait for any errors to accumulate
            this.currentThrottleTimeout = setTimeout(() => {
                const recs = Object.keys(this.records).map(errKey => this.records[errKey]);
                if(recs.length) {
                    const xhr = new XMLHttpRequest();
                    xhr.onreadystatechange = () => {
                        if(xhr.readyState === XMLHttpRequest.DONE) {
                            if(xhr.status >= 400) {
                                if(typeof onError === 'function') {
                                    onError.call(this, recs, xhr);
                                } else {
                                    console.warn('Browser Bunyan: A server log write failed');
                                }
                            }
                            this.records = {};
                            throttleRequests();
                        }
                    };
                    xhr.open(method, url);
                    xhr.setRequestHeader('Content-Type', 'application/json');
                    xhr.withCredentials = withCredentials;
                    xhr.send(JSON.stringify(recs));
                } else {
                    throttleRequests();
                }
            }, throttleInterval);
        };

        throttleRequests();
    }

    stop() {
        setTimeout(() => {
            if(this.currentThrottleTimeout) {
                clearTimeout(this.currentThrottleTimeout);
                this.currentThrottleTimeout = null;
            }
        }, 1);
    }

    write(rec) {
        rec.url = typeof window !== 'undefined' && window.location.href;
        rec.userAgent = userAgent;
        if(this.currentThrottleTimeout && this.writeCondition(rec)) {
            if(this.records[rec.msg]) {
                this.records[rec.msg].count++;
            } else {
                rec.count = 1;
                this.records[rec.msg] = rec;
            }
        }
    }

    static defaultWriteCondition() {
        return window.navigator.onLine && !isBot;
    }
}

Will release this as a separate module for browser-bunyan 2.x

I was using this method with slight changes.
Beware that if array gets deleted while new items are added these items will get lost.
you should use an array and change to array.splice(0, array.length) copying it to a temporary array so new values won't get lost in transaction.

kindly regards

// [...]
this.records = []; // use an array instead

    this.start();
  }

  start() {
    const { throttleInterval = 3000, client } = this.opts;

    const throttleRequests = () => {
      // wait for any errors to accumulate
      this.currentThrottleTimeout = setTimeout(() => {
        const recs = this.records.splice(0, this.records.length); // create a copy of current values, empty this.records
        if (recs.length > 0) { // check temparray isn't empty
          // [...] some client logic
           if(fail) {
              // add tmp array back to array (reschedule)
              this.records.splice(0, 0, ...recs);
           }
          }
          throttleRequests();
        } else {
          throttleRequests();
        }
      }, throttleInterval);
    };

    throttleRequests();
  }