You can format ISO Date by JavaScript functions as follows:

// Create element:
var todayDate = new Date().toISOString();
const dateField = document.createElement("p");
dateField.innerText = new Date().toISOString().split('.')[0].split('T').join(' ');

// Append to body:
document.body.appendChild(dateField);

// Output: 2022-07-17 16:31:22

You should use built-in Date object in Javascript, like this:

let currentdate = new Date(); 
let datetime = currentdate.getFullYear() + "-"
                + String((currentdate.getMonth() + 1)).padStart(2,"0")  + "-" 
                + String(currentdate.getDate()).padStart(2,"0") + " "
                + String(currentdate.getHours()).padStart(2,"0") + ":"  
                + String(currentdate.getMinutes()).padStart(2,"0") + ":" 
                + String(currentdate.getSeconds()).padStart(2,"0");
//The `+1` on the getMonth() is used because in Javascript January is 0.
console.log(datetime);

By the way, I suggest you make all your vars into lets as that's the current standard. There's a very fine difference between them (let is block scoped while var is functional scoped).