Javascript - Arguments and Closures

closure.js

function add() {
    if(arguments.length > 1){
        return Array.from(arguments).every(function(val){
            return typeof val === 'number';	
        }) ? Array.from(arguments).reduce(function(prev, current){
            return prev + current
        }) : undefined;
    }else if(typeof arguments[0] === 'number'){
        var x = arguments[0];
    	return function(y){
        	return typeof y === 'number' ? x + y : undefined;
        }
    }else {
      return undefined
    }
}

//all data types besides number will return undefined
  //add('2') --> undefined
  //add(2,'3') --> undefined
  
var addToAdd = add(2);
addToAdd(7); // closure example