RSI Javascript relative strenght index node nodejs

rsi.js

const inputs = { rsi: 8 };

main['rsi_' + pair] = generateRSI(pair);

const generateRSI = pair => {

    const closes = main.closes[pair];
    const len = closes.length;
    const arr = [];
    let prevAvgGain = 0, prevAvgLoss = 0;
    
    for (let j = 250 + inputs.rsi; j > 250; j--) { // first run 
        
        let losses = 0, gains = 0;
        const previous = closes[len - (j + 1)]; // -259
        const present = closes[len - j]; // -258

        if (previous < present) gains += present - previous // If price went up, add gain amount
        else if (previous > present) losses += previous - present // If price went down, add loss amount

        prevAvgGain = gains / inputs.rsi;
        prevAvgLoss = losses / inputs.rsi;
    }

    for (let i = 250; i > 0; i--) {

        let loss = 0, gain = 0;
        const previous = closes[len - (i + 1)];
        const present = closes[len - i]; 

        if (previous < present) gain = present - previous;
        else if (previous > present) loss = previous - present;

        prevAvgGain = (prevAvgGain * (inputs.rsi - 1) + gain) / inputs.rsi;
        prevAvgLoss = (prevAvgLoss * (inputs.rsi - 1) + loss) / inputs.rsi;

        const rs = prevAvgGain / prevAvgLoss;
        arr.push(100 - (100 / (1 + rs)));
    }
    return arr;
};