type="number" but still requires a text to number conversion

Question

I've an element (x) of type=number. In my work to verify it's value is a number before performing mathematical operations I've concluded that elements of type "number", while having builtin validation and helpful input controls, still assign their values as text and will require a conversion to number before performing mathematical operations. My question - Is this true or is there something wrong in my code? Here's my work. Entered the number 6.

        x = document.createElement("input");
        x.type = "number";
        x.step = "0.1";
        x.min = "0";
        x.max = "9999";
        x.defaultValue = "1";

var p = document.getElementById(x.id).value;
isThisNumber(p);


function isThisNumber(z) {
    alert(typeof z + " --- " + typeof (z));  // returns "string --- string"

    if (z.isNaN) {
        alert("it's not number");
    } else {
        alert("it's a number");  // returns false - it's a number
    }

    if (z.toFixed) {
        alert("it's a number");
    } else {
        alert("it's not a number");  // returns false - it's not a number
    }

    var a = z + z;
    alert("sum is : " + a);  // returns "66"

    var b = Number(z);
    var b2 = b + b;
    alert("sum is : " + b2);  // returns "12"
}

Ref: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/number