JSFiddle - React, Tailwind, and code Playground

JavaScript

function flatten() {
    var result = [];
    for (var i = 0, length = arguments.length; i < length; i++) {
        if (Array.isArray(arguments[i])) {
           result = result.concat(arguments[i]);
        } else {
            result.push(arguments[i]);
        }
    }
    return result;
}

console.log(flatten("Text", [1,2]));
console.log(flatten(1,4 ,[4,6,8]));
console.log(flatten(1, 2, 3, 4, 5));
console.log(flatten([1, 2, 3], [4, 5, 6]));
console.log(flatten([1, 2, 3], [4, [5, 6]])); // sosnooley