Calculating median - javascript

I've been trying to calculate median but still I've got some mathematical issues I guess as I couldn't get the correct median value and couldn't figure out why. Here's the code;

class StatsCollector {

    constructor() {
        this.inputNumber = 0;
        this.average = 0;

        this.timeout = 19000;

        this.frequencies = new Map();
        for (let i of Array(this.timeout).keys()) {
            this.frequencies.set(i, 0);
        }
    }

    pushValue(responseTimeMs) {
        let req = responseTimeMs;
        if (req > this.timeout) {
            req = this.timeout;
        }

        this.average = (this.average * this.inputNumber + req) / (this.inputNumber + 1);

        console.log(responseTimeMs / 1000)
        let groupIndex = Math.floor(responseTimeMs / 1000);
        this.frequencies.set(groupIndex, this.frequencies.get(groupIndex) + 1);

        this.inputNumber += 1;
    }

    getMedian() {
        let medianElement = 0;
        if (this.inputNumber <= 0) {
            return 0;
        }
        if (this.inputNumber == 1) {
            return this.average
        }
        if (this.inputNumber == 2) {
            return this.average
        }
        if (this.inputNumber > 2) {
            medianElement = this.inputNumber / 2;
        }

        let minCumulativeFreq = 0;
        let maxCumulativeFreq = 0;
        let cumulativeFreq = 0;
        let freqGroup = 0;
        for (let i of Array(20).keys()) {
            if (medianElement <= cumulativeFreq + this.frequencies.get(i)) {
                minCumulativeFreq = cumulativeFreq;
                maxCumulativeFreq = cumulativeFreq + this.frequencies.get(i);
                freqGroup = i;
                break;
            }
            cumulativeFreq += this.frequencies.get(i);
        }

        return (((medianElement - minCumulativeFreq) / (maxCumulativeFreq - minCumulativeFreq)) + (freqGroup)) * 1000;
    }

    getAverage() {
        return this.average;
    }

}

Here's the snapshot of the results when I enter the values of

342,654,987,1093,2234,6243,7087,20123

The correct result should be;

Median: 1663.5

Change your median method to this:

function median(values: number[]): number {

  if (values.length === 0) {
    throw new Error('Input array is empty');
  }

  // Sorting values, preventing original array
  // from being mutated.
  values = [...values].sort((a, b) => a - b);

  const half = Math.floor(values.length / 2);

  return (values.length % 2
    ? values[half]
    : (values[half - 1] + values[half]) / 2
  );

}

fiddle