an example on how to create pipe functions that behave nicely when used

sum-pipe.js

function sum(initialValue) {
    // we need both of these here to allow returning
    // the result if no number was added
    innerSum.result = initialValue;
    innerSum.toString = () => innerSum.result;

    return innerSum;

    function innerSum(addedValue) {
        innerSum.result += addedValue;
        return innerSum;
    }
}

console.log(sum(2)(3)(4)); // 9 f (will print 9 but will note this is a function)
console.log(sum(2)(3)(4).result); // 9 (result returns an actual number)
console.log(sum(2)(3)(4) + 100); // 109 (when performing addition, toString is called)

let runningSummary = sum(5);

runningSummary(5)(40)(-5);

console.log(runningSummary); // 45 f
console.log(runningSummary.result); // 45