How to get all selected option text form multi select Using Javascript

// Return an array of the selected opion values
// select is an HTML select element
function GetSelectValues(select) {
  var result = [];
  var options = select && select.options;
  var opt;

  for (var i=0, iLen=options.length; i<iLen; i++) {
    opt = options[i];

    if (opt.selected) {
      result.push(opt.value || opt.text);
    }
  }
  return result;
}

pass this function your select box as like..

var selectBox = document.getElementsById('fm_delivery_or_collection');
alert(GetSelectValues(selectBox ));

it will return the array of selected values

By using Jquery

$('select#fm_delivery_or_collection').val()

the val function called from the select will return an array if its a multiple.

Your comment please suggest me how can i get all selected option text, So you can try this:

$("#fm_delivery_or_collection option:selected").each(function () {
   var $this = $(this);
   if ($this.length) {
    var selText = $this.text();
    console.log(selText);
   }
});

do all in one line now

var text = $('#selector option:selected').toArray().map(item => item.text).join();

it return like this:

text1,text2,text3,text4

Try with this

$("#fm_delivery_or_collection option").each(function(){
    if($(this).attr('selected') == 'selected')
    {
        var name = $("#fm_delivery_or_collection").attr('name')
        var str1 = $("#fm_delivery_or_collection").attr('id').replace("fm_"," ")
        requestString += "<b>"+str1.replace(/_/g," ")+"</b>" + ':' +strUser+"<br>";
     }
})