botstarFormatNumbers.js

//input & output variables definition
let input_var  = event.conversation.variables.YOUR_VARIABLE_HERE; //your input variable name
let output_var = "YOUR_VARIABLE_HERE"; //your output variable name

// Decimals to show
// 2 --> currency format
// 1 --> percentage format
const decimals_to_show = 2; //change this value

//---------------------------------------------------
//---------------------------------------------------
function show_decimals(input_number, decimals){
	let formated_number = new Intl.NumberFormat('en-US',{useGrouping: false,  
                                             maximumFractionDigits: decimals}).format(input_number);
	return formated_number;
}

let mapping = {};
mapping[output_var] = show_decimals(input_var, decimals_to_show);  
let doneObj = {
        "actions": [{
          "type": "set_variable",
          "data": mapping
        }]
      };
done(doneObj);