ma.js

module.exports = {

    EMA: function(originalArray, emaLength) {
        let array = originalArray.slice().reverse(); // easier on my limited brain to think of the array in the "proper" order
        // trim initial NaN values
        let iPos = 0;
        for (iPos = 0; iPos < array.length && isNaN(array[iPos]); iPos++) {
        }
        array = array.slice(iPos);// trim initial NaN values from array
        let ema = [];
        const k = 2 / (emaLength + 1);
        for (let i = 0; i < emaLength - 1; i++) {
            ema[i] = NaN;
        }

        // console.log(originalArray[0]);
        // notice improperly formatted data bugs out here, have to JSON.parse to remove "

        ema[emaLength - 1] = array.slice(0, emaLength).reduce(function (a, b) {
            return a + b
        }) / emaLength;
        for (let i = emaLength; i < array.length; i++) {
            ema[i] = array[i] * k + ema[i - 1] * (1 - k);
        }
        ema.reverse();// reverse back for main consumption
        for (let i = 0; i < iPos; i++) {
            ema.push(NaN);
        }
        return ema;
    },

    MACD: function(array, i12, i26, i9, oCandle) {

        const ema12 = module.exports.EMA(oCandle.c, i12);
        const ema26 = module.exports.EMA(oCandle.c, i26);
        const macd = [];
        for (let i = 0; i < ema12.length; i++) {
            macd.push(ema12[i] - ema26[i]);
        }
        const signal = module.exports.EMA(macd, i9);
        const histogram = [];
        for (let i = 0; i < macd.length; i++) {
            histogram.push(macd[i] - signal[i]);
        }
        return {macd: macd, signal: signal, histogram: histogram};
    },
    SMA: function( array, smaLength ){

        array.reverse(); // easier on my limited brain to think of the array in the "proper" order
        let sma = [];
        for (let i=0; i<smaLength-1; i++){
            sma[i] = NaN;
        }
        sma[smaLength-1] = array.slice(0,smaLength).reduce(function(a, b) { return a + b }) / smaLength;
        for(let i=smaLength; i<array.length; i++){
            sma[i] = sma[i-1] + (array[i] - array[i-smaLength]) / smaLength;
        }
        sma.reverse();// reverse back for main consumption
        array.reverse();// reverse back
        return sma;
    }
};