JSFiddle - React, Tailwind, and code Playground

JavaScript

function steamroll(arr){
var arr0=[];
var printArray = function(arr) {
if (Array.isArray(arr)){
for (i=0;i<arr.length;i++){
printArray(arr[i]);
}
}
else {arr0.push(arr)}
};
printArray(arr);
return arr0;
}

steamroll([1,[2,[3,4]]]);