Optimise custom function with multiple args to accept ranges - google-apps-script

Question

The developers guide of google apps suggests to write your function to accept ranges for optimization like this:
function DOUBLE(input) {
if (input.map) { // Test whether input is an array.
return input.map(DOUBLE); // Recurse over array if so.
} else {
return input * 2;
}
}
I wonder how you would that with multiple arguments?
e.g
function DOUBLEandADD(doubleThis, addThis){
return (doubleThis * 2) + addThis;
}
Do you check both at once and how do you iterate over the ranges?
Something like this perhaps?
function DOUBLEandADD(doubleThis, addThis) {
if (doubleThis.map && addThis.map){
var d = Array.from(doubleThis.values());
var a = Array.from(addThis.values());
for (var i = 0; i < d.length(); i++){
return DOUBLEandADD(d[i],a[i]);
}
} else {
return (doubleThis * 2) + addThis;
}
}

Answer 1

You would wrap the the map function in an anonymous function and pass the additional parameters.
function DOUBLEandADD(input,addend) {
if (input.map) {
return input.map(function(i){return DOUBLEandADD(i,addend)});
} else {
return (input * 2) + addend;
}
}

Answer 2

I wouldn't use map in your case. How about this:
function DOUBLEandADD(doubleThis, addThis) {
if (Array.isArray(doubleThis) || Array.isArray(addThis)) {
if (!Array.isArray(doubleThis) ||
!Array.isArray(addThis) ||
doubleThis.length != addThis.length) {
throw new Error("doubleThis and addThis arrays must be same length.");
}
var results = [];
for (var i = 0; i < doubleThis.length; i++) {
results.push((doubleThis[i] * 2) + addThis[i]);
}
return results;
} else {
return (doubleThis * 2) + addThis;
}
}