Double EMA

There are several indicators that employ two moving averages with different periods. We'll build some variation of it and will show two EMA side-by-side. Let's call one of them "fast EMA" and another "slow EMA".

As in the previous indicator, we will apply the ready-to-use EMA algorithm from tools. Twice. And each EMA will have its own parameter and own output value.

To return two values from our Calculator.map function implementation, we will return an object with two fields instead of just a number as previously. Then, we will define how to plot these values and will refer to their names.

const predef = require("./tools/predef");
const EMA = require("./tools/EMA");

class doubleEma {
   init() {
       this.slowEma = EMA(this.props.slowPeriod);
       this.fastEma = EMA(this.props.fastPeriod);
   }

   map(d) {
       const value = d.value();
       return {
           slow: this.slowEma(value),
           fast: this.fastEma(value)
       };
   }
}

module.exports = {
   name: "doubleEma",
   description: "Double EMA",
   calculator: doubleEma,
   params: {
       slowPeriod: predef.paramSpecs.period(21),
       fastPeriod: predef.paramSpecs.period(10)
   },
   tags: ["My Indicators"],
   plots: {
       fast: { title: "FastEMA" },
       slow: { title: "SlowEMA" },
   },
   schemeStyles: {
       dark: {
           fast: {color: "red"},
           slow: {color: "blue", lineStyle: 3 }
       }
   }
};

Now module's export includes a new field Indicator.plots: it tells the app which fields from the output object should be plotted and shown in the Data Box inside Charts.

This version of Indicator.schemeStyles includes default line properties for both these plots.