Converting Option set into CheckBox

function Form_onload() {

    var optionset = document.getElementById("optionset_schema_name");
    var multiline = document.getElementById("multiline_schema_name");

    if (optionset != null && multiline != null) {

        optionset.style.display = "none";            //"none" represents override of existing, the optionset field is overrided
        var pdiv = document.createElement('div');    //Create an element
        pdiv.style = 'overflow-y:auto; height:100px; border:2px #6699cc solid; background-color:#ffffff;';
        //overflow y represents vertical scroll bar for options if options are more which will display if options are more.

        optionset.parentNode.appendChild(pdiv);

        // Convert option set to check box

        for (var i = 1; i < optionset.options.length; i++) {
            var OptionSetItems = optionset.options[i];
            if (!IsChecked(OptionSetItems.text, multiline)) {
                var addInput = document.createElement('input');
                addInput.type = 'checkbox';
                addInput.style.pixelWidth = 30;
            }
            else {
                var addInput = document.createElement('input');
                addInput.type = 'checkbox';
                addInput.checked = true;
                addInput.style.pixelWidth = 30;
            }

            var addLabel = document.createElement('label');
            addLabel.innerText = OptionSetItems.text;
            var addBr = document.createElement('br');
       
            optionset.nextSibling.appendChild(addInput);
            optionset.nextSibling.appendChild(addLabel);
            optionset.nextSibling.appendChild(addBr);

        }
    }
}

// To check if which check box is selected
function IsChecked(pText, multiline) {
    if (multiline.value != "") {
        var multiline = multiline.value.split(",");
        for (var i = 0; i <multiline.length; i++) {
            if (multiline[i] == pText)
                return true;
        }
    }
    return false;
}

//On Save Code
//---------------->
 function Form_onSave() {
 
    var optionset = document.getElementById("optionset_schema_name");
 
    var multiline = "";
    var getInput = optionset.nextSibling.getElementsByTagName("input");

    for (var i = 0; i < getInput.length; i++) {
        if (getInput[i].checked) {
            multiline += getInput[i].nextSibling.innerText + ",";
            //placing all the options into multiline of text
        }
    }
    Xrm.Page.getAttribute("multiline_schema_name").setValue(multiline);

}