How to get all selected values of a multiple select box?

With jQuery, the usual way:

var values = $('#select-meal-type').val();

From the docs:

In the case of <select multiple="multiple"> elements, the .val() method returns an array containing each selected option;

You can use selectedOptions property

var options = document.getElementById('select-meal-type').selectedOptions;
var values = Array.from(options).map(({ value }) => value);
console.log(values);

<select id="select-meal-type" multiple="multiple">
    <option value="1">Breakfast</option>
    <option value="2" selected>Lunch</option>
    <option value="3">Dinner</option>
    <option value="4" selected>Snacks</option>
    <option value="5">Dessert</option>
</select>

Actually, I found the best, most-succinct, fastest, and most-compatible way using pure JavaScript (assuming you don't need to fully support IE lte 8) is the following:

var values = Array.prototype.slice.call(document.querySelectorAll('#select-meal-type option:checked'),0).map(function(v,i,a) { 
    return v.value; 
});

An even more succinct way using ES6/ES2015 (for the browsers that support it):

const selected = document.querySelectorAll('#select-meal-type option:checked');
const values = Array.from(selected).map(el => el.value);

ES6

[...select.options].filter(option => option.selected).map(option => option.value)

Where select is a reference to the <select> element.

To break it down:

• [...select.options] takes the Array-like list of options and destructures it so that we can use Array.prototype methods on it (Edit: also consider using Array.from())
• filter(...) reduces the options to only the ones that are selected
• map(...) converts the raw <option> elements into their respective values

If you wanna go the modern way, you can do this:

const selectedOpts = [...field.options].filter(x => x.selected);

The ... operator maps iterable (HTMLOptionsCollection) to the array.

If you're just interested in the values, you can add a map() call:

const selectedValues = [...field.options]
                     .filter(x => x.selected)
                     .map(x => x.value);

First, use Array.from to convert the HTMLCollection object to an array.

let selectElement = document.getElementById('categorySelect')
let selectedValues = Array.from(selectElement.selectedOptions)
        .map(option => option.value) // make sure you know what '.map' does

// you could also do: selectElement.options

$('#select-meal-type :selected') will contain an array of all of the selected items.

$('#select-meal-type option:selected').each(function() {
    alert($(this).val());
});

Suppose the multiSelect is the Multiple-Select-Element, just use its selectedOptions Property:

//show all selected options in the console:

for ( var i = 0; i < multiSelect.selectedOptions.length; i++) {
  console.log( multiSelect.selectedOptions[i].value);
}

Pretty much the same as already suggested but a bit different. About as much code as jQuery in Vanilla JS:

selected = Array.prototype.filter.apply(
  select.options, [
    function(o) {
      return o.selected;
    }
  ]
);

It seems to be faster than a loop in IE, FF and Safari. I find it interesting that it's slower in Chrome and Opera.

Another approach would be using selectors:

selected = Array.prototype.map.apply(
    select.querySelectorAll('option[selected="selected"]'),
    [function (o) { return o.value; }]
);

Check this:

HTML:

<select id="test" multiple>
<option value="red" selected>Red</option>
<option value="rock" selected>Rock</option>
<option value="sun">Sun</option>
</select>

Javascript one line code

Array.from(document.getElementById("test").options).filter(option => option.selected).map(option => option.value);

Update October 2019

The following should work "stand-alone" on all modern browsers without any dependencies or transpilation.

<!-- display a pop-up with the selected values from the <select> element -->

<script>
 const showSelectedOptions = options => alert(
   [...options].filter(o => o.selected).map(o => o.value)
 )
</script>

<select multiple onchange="showSelectedOptions(this.options)">
  <option value='1'>one</option>
  <option value='2'>two</option>
  <option value='3'>three</option>
  <option value='4'>four</option>
</select>

If you need to respond to changes, you can try this:

document.getElementById('select-meal-type').addEventListener('change', function(e) {
    let values = [].slice.call(e.target.selectedOptions).map(a => a.value));
})

The [].slice.call(e.target.selectedOptions) is needed because e.target.selectedOptions returns a HTMLCollection, not an Array. That call converts it to Array so that we can then apply the map function, which extract the values.

if you want as you expressed with breaks after each value;

$('#select-meal-type').change(function(){
    var meals = $(this).val();
    var selectedmeals = meals.join(", "); // there is a break after comma

    alert (selectedmeals); // just for testing what will be printed
})

Try this:

$('#select-meal-type').change(function(){
    var arr = $(this).val()
});

Demo

$('#select-meal-type').change(function(){
  var arr = $(this).val();
  console.log(arr)
})

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<select id="select-meal-type" multiple="multiple">
  <option value="1">Breakfast</option>
  <option value="2">Lunch</option>
  <option value="3">Dinner</option>
  <option value="4">Snacks</option>
  <option value="5">Dessert</option>
</select>

fiddle

Here is an ES6 implementation:

value = Array(...el.options).reduce((acc, option) => {
  if (option.selected === true) {
    acc.push(option.value);
  }
  return acc;
}, []);

Building on Rick Viscomi's answer, try using the HTML Select Element's selectedOptions property:

let txtSelectedValuesObj = document.getElementById('txtSelectedValues');
[...txtSelectedValuesObj.selectedOptions].map(option => option.value);

In detail,

• selectedOptions returns a list of selected items.
• Specifically, it returns a read-only HTMLCollection containing HTMLOptionElements.
• ... is spread syntax. It expands the HTMLCollection's elements.
• [...] creates a mutable Array object from these elements, giving you an array of HTMLOptionElements.
• map() replaces each HTMLObjectElement in the array (here called option) with its value (option.value).

Dense, but it seems to work.

Watch out, selectedOptions isn't supported by IE!

Something like the following would be my choice:

let selectElement = document.getElementById('categorySelect');
let selectedOptions = selectElement.selectedOptions || [].filter.call(selectedElement.options, option => option.selected);
let selectedValues = [].map.call(selectedOptions, option => option.value);

It's short, it's fast on modern browsers, and we don't care whether it's fast or not on 1% market share browsers.

Note, selectedOptions has wonky behavior on some browsers from around 5 years ago, so a user agent sniff isn't totally out of line here.

You can get as an array the values from the <select> at the submit of the form as this example :

const form = document.getElementById('form-upload');

form.addEventListener('change', (e) => {
    const formData = new FormData(form);
    const selectValue = formData.getAll('pets');
    console.log(selectValue);
})

<form id="form-upload">
  <select name="pets" multiple id="pet-select">
      <option value="">--Please choose an option--</option>
      <option value="dog">Dog</option>
      <option value="cat">Cat</option>
      <option value="hamster">Hamster</option>
      <option value="parrot">Parrot</option>
      <option value="spider">Spider</option>
      <option value="goldfish">Goldfish</option>
  </select>
</form>

You Can try this script

     <!DOCTYPE html>
    <html>
    <script>
    function getMultipleSelectedValue()
    {
      var x=document.getElementById("alpha");
      for (var i = 0; i < x.options.length; i++) {
         if(x.options[i].selected ==true){
              alert(x.options[i].value);
          }
      }
    }
    </script>
    </head>
    <body>
    <select multiple="multiple" id="alpha">
      <option value="a">A</option>
      <option value="b">B</option>
      <option value="c">C</option>
      <option value="d">D</option>
    </select>
    <input type="button" value="Submit" onclick="getMultipleSelectedValue()"/>
    </body>
    </html>

You can use [].reduce for a more compact implementation of RobG's approach:

var getSelectedValues =  function(selectElement) {
  return [].reduce.call(selectElement.options, function(result, option) {
    if (option.selected) result.push(option.value);
    return result;
  }, []);
};

My template helper looks like this:

 'submit #update': function(event) {
    event.preventDefault();
    var obj_opts = event.target.tags.selectedOptions; //returns HTMLCollection
    var array_opts = Object.values(obj_opts);  //convert to array
    var stray = array_opts.map((o)=> o.text ); //to filter your bits: text, value or selected
    //do stuff
}

Same as the earlier answer but using underscore.js.

function getSelectValues(select) {
    return _.map(_.filter(select.options, function(opt) { 
        return opt.selected; }), function(opt) { 
            return opt.value || opt.text; });
}

Works everywhere without jquery:

var getSelectValues = function (select) {
    var ret = [];

    // fast but not universally supported
    if (select.selectedOptions != undefined) {
        for (var i=0; i < select.selectedOptions.length; i++) {
            ret.push(select.selectedOptions[i].value);
        }

    // compatible, but can be painfully slow
    } else {
        for (var i=0; i < select.options.length; i++) {
            if (select.options[i].selected) {
                ret.push(select.options[i].value);
            }
        }
    }
    return ret;
};

Here ya go.

const arr = Array.from(el.features.selectedOptions) //get array from selectedOptions property
const list = [] 
arr.forEach(item => list.push(item.value)) //push each item to empty array
console.log(list)

Simply use this single line of code: (without JQuery)

const category_ids = Array.from(document.querySelectorAll('#category_id option:checked')).map(option => option.value);
console.log('category_ids: ', category_ids);

You can create your own function like this and use it everywhere

JavaScript:

/**
* Get values from multiple select input field
* @param {string} selectId - the HTML select id of the select field
**/
function getMultiSelectValues(selectId) {
 // get the options of select field which will be HTMLCollection
 // remember HtmlCollection and not an array. You can always enhance the code by
 // verifying if the provided select is valid or not
  var options = document.getElementById(selectId).options; 
    var values = [];
    
   // since options are HtmlCollection, we convert it into array to use map function on it
    Array.from(options).map(function(option) {
        option.selected ? values.push(option.value) : null
    })

    return values;
}

you can get the same result using jQuery in a single line

$('#select_field_id').val()

and this will return the array of values of well.

1. $('#application_student_groups option:selected') returns a collection of selected objects
2. .toArray() returns the selected objects in an array
3. And in map I return the option value (or you can return text) from the array.

$('#application_student_groups option:selected').toArray().map(item => item.value)