Trimmed Mean and Median in ES6.

trimmedMean.js

const mean = (values) => {
    let sum = values.reduce((previous, current) => current += previous);
    return sum / values.length;
};

const median = (arr) => {
    const mid = Math.floor(arr.length / 2);
    const sorted = [...arr].sort((a, b) => a - b);
    return arr.length % 2 == 0 ?  (sorted[mid - 1] + sorted[mid]) / 2 : sorted[mid];
};

const trimmedMean = (values, trimAmount) => {
    var trimCount = Math.floor(trimAmount*values.length);
    return mean(values.sort((a, b) => a - b).slice(trimCount, values.length-trimCount));
};