how to add currency pattern to input element while typing in javascript?

function setFormat(id,separator) {
    let element = document.getElementById(id)
    let sepRegex = new RegExp(separator, 'g');
    let value = element.value.replace(sepRegex, ""); 

    if (!isNaN(value) && value != "") {
        var formattedValue = value.replace(/\B(?=(\d{3})+(?!\d))/g, separator);
        element.value= formattedValue; 
    }
}

#currency {
  text-align: left;
  direction: ltr;
}

<input type="text" id="currency" oninput="setFormat(this.id,'/')" >