Javascript: check if exist a variable with dynamic name

I have a problem with my JavaScript code.

I want to check if a variable with dynamic name exist, but I don't know how to do it. I tried to do something, but it doesn't work

If someone could help me, I would be very grateful. Thx, Alessio

function addElement(id_sub, id_v){
    var n_id_sub = document.getElementById('sub'+id_sub).value;
    var name = "tot" + id_sub;
    checkName(name);
    var n_prod = document.getElementById('number'+id_v).value;
    if(n_prod>=2){
        alert(n_prod)
    }else{
        var inputField=document.getElementById('number'+id_v);
        inputField.value=parseInt(n_prod)+1;
        
    }
}

function checkName(n){
    if(typeof window['name'] === 'undefined'){
        var window['name'] = 0;
    } 
}

EDIT: Sorry, I didn't make myself clear, I'm currently studying to improve my English. I want to create a js file that retrieve a value from an HTML form. I need to check if there is a variable that has the retrieved value as its name.