JSFiddle - React, Tailwind, and code Playground

JavaScript

slice=Function.prototype.call.bind([].slice);
function add(x){
    var args=slice(arguments);
    if(args.length>1) return args[0]+args[1];
    return function(y){
        return x+y;
    }
}

console.log(add(3)(4));
console.log(add(3,5));