Javascript to Select Multiple options

Question

I have a form with a select box that allows multiple options. After a user saves these options, it stores them in a database table.

I can then read this database table to get the options they chose one again. I need to be able to grab this data from the database, put it into an array, then have the options in that select box to be pre-selected when they go to "Edit" their options.

Reading the data into an array is fine, and I know how to make a single option selected within a select box, however I'm not sure how to handle multiple options being selected in javascript.

Can someone help me figure out the javascript required to do this?

Answer 1

A pure javascript solution

<select id="choice" multiple="multiple">
  <option value="1">One</option>
  <option value="2">two</option>
  <option value="3">three</option>
</select>
<script type="text/javascript">

var optionsToSelect = ['One', 'three'];
var select = document.getElementById( 'choice' );

for ( var i = 0, l = select.options.length, o; i < l; i++ )
{
  o = select.options[i];
  if ( optionsToSelect.indexOf( o.text ) != -1 )
  {
    o.selected = true;
  }
}

</script>

Although I agree this should be done server-side.

Answer 2

This type of thing should be done server-side, so as to limit the amount of resources used on the client for such trivial tasks. That being said, if you were to do it on the front-end, I would encourage you to consider using something like underscore.js to keep the code clean and concise:

var values = ["Red", "Green"],
    colors = document.getElementById("colors");

_.each(colors.options, function (option) {
    option.selected = ~_.indexOf(values, option.text);
});

If you're using jQuery, it could be even more terse:

var values = ["Red", "Green"];

$("#colors option").prop("selected", function () {
    return ~$.inArray(this.text, values);
});

If you were to do this without a tool like underscore.js or jQuery, you would have a bit more to write, and may find it to be a bit more complicated:

var color, i, j,
    values = ["Red", "Green"],
    options = document.getElementById("colors").options;

for ( i = 0; i < values.length; i++ ) {
    for ( j = 0, color = values[i]; j < options.length; j++ ) {
        options[j].selected = options[j].selected || color === options[j].text;
    }
}

Answer 3

You can get access to the options array of a selected object by going document.getElementById("cars").options where 'cars' is the select object.

Once you have that you can call option[i].setAttribute('selected', 'selected'); to select an option.

I agree with every one else that you are better off doing this server side though.

Answer 4

<script language="JavaScript" type="text/javascript">
<!--
function loopSelected()
{
  var txtSelectedValuesObj = document.getElementById('txtSelectedValues');
  var selectedArray = new Array();
  var selObj = document.getElementById('selSeaShells');
  var i;
  var count = 0;
  for (i=0; i<selObj.options.length; i++) {
    if (selObj.options[i].selected) {
      selectedArray[count] = selObj.options[i].value;
      count++;
    }
  }
  txtSelectedValuesObj.value = selectedArray;
}
function openInNewWindow(frm)
{
  // open a blank window
  var aWindow = window.open('', 'Tutorial004NewWindow',
   'scrollbars=yes,menubar=yes,resizable=yes,toolbar=no,width=400,height=400');

  // set the target to the blank window
  frm.target = 'Tutorial004NewWindow';

  // submit
  frm.submit();
}
//-->
</script>
The HTML
<form action="tutorial004_nw.html" method="get">
  <table border="1" cellpadding="10" cellspacing="0">
  <tr>
    <td valign="top">
      <input type="button" value="Submit" onclick="openInNewWindow(this.form);" />
      <input type="button" value="Loop Selected" onclick="loopSelected();" />
      <br />
      <select name="selSea" id="selSeaShells" size="5" multiple="multiple">
        <option value="val0" selected>sea zero</option>
        <option value="val1">sea one</option>
        <option value="val2">sea two</option>
        <option value="val3">sea three</option>
        <option value="val4">sea four</option>
      </select>
    </td>
    <td valign="top">
      <input type="text" id="txtSelectedValues" />
      selected array
    </td>
  </tr>
  </table>
</form>

Answer 5

Based on @Peter Baley answer, I created a more generic function:

   @objectId: HTML object ID
   @values: can be a string or an array. String is less "secure" (should not contain repeated value).
   function checkMultiValues(objectId, values){
        selectMultiObject=document.getElementById(objectId);
        for ( var i = 0, l = selectMultiObject.options.length, o; i < l; i++ )
        {
          o = selectMultiObject.options[i];
          if ( values.indexOf( o.value ) != -1 )
          {
            o.selected = true;
          } else {
            o.selected = false;
          }
        }
    }

Example: checkMultiValues('thisMultiHTMLObject','a,b,c,d');