How can I get my code to check if I entered in an integer?

Question

My code isn't working on my JavaScript project. I want it to check if you inputted an integer or not, and if you did, check if you inputted a whole number. I expected it to accept the number "3" in my prompt and say it was an integer. Instead, everything I put in "isn't an integer." Can someone help? Here's a copy of my code:

function changeTime() {
    var changeTimee = prompt("Enter in a new amount of seconds. Leave blank or press cancel to cancel.");
    console.log("You entered: " + changeTimee);
    if (Number.isInteger(changeTimee)) {
        if (floor(changeTimee) === changeTimee) {
        if (changeTimee === "" || changeTimee === null) {
            console.log("Left Blank");
        } else {
            seconds = changeTimee;
        }
        }
    } else {
        alert("Please enter positive integer, not a string.");
    }
    console.log(seconds);
}