[javascript] How do I change an HTML selected option using JavaScript?

I have option menu like this:

<form name="AddAndEdit">
   <select name="list" id="personlist">
      <option value="11">Person1</option>
      <option value="27">Person2</option>
      <option value="17">Person3</option>
      <option value="10">Person4</option>
      <option value="7">Person5</option>
      <option value="32">Person6</option>
      <option value="18">Person7</option>
      <option value="29">Person8</option>
      <option value="28">Person9</option>
      <option value="34">Person10</option>
      <option value="12">Person11</option>
      <option value="19">Person12</option>
   </select>
</form>

And now I want to change the selected option by using an href. For example:

<a href="javascript:void(0);"
  onclick="document.getElementById('personlist').getElementsByTagName('option')[11].selected = 'selected';">change</a>

But I want to select the option with value=11 (Person1), not Person12.

How do I change this code?

You can use JQuery also

$(document).ready(function () {
  $('#personlist').val("10");
}

You could also change select.options.selectedIndex DOM attribute like this:

function selectOption(index){ _x000D_
  document.getElementById("select_id").options.selectedIndex = index;_x000D_
}

<p>_x000D_
<select id="select_id">_x000D_
  <option selected>first option</option>_x000D_
  <option>second option</option>_x000D_
  <option>third option</option>_x000D_
</select>_x000D_
</p>_x000D_
<p>_x000D_
  <button onclick="selectOption(0);">Select first option</button>_x000D_
  <button onclick="selectOption(1);">Select second option</button>_x000D_
  <button onclick="selectOption(2);">Select third option</button>_x000D_
</p>

It's an old post, but if anyone is still looking for solution to this kind of problem, here is what I came up with:

<script>
  document.addEventListener("DOMContentLoaded", function(e) {
    document.forms['AddAndEdit'].elements['list'].value = 11;
  });
</script>

I believe that the blog post JavaScript Beginners – Select a dropdown option by value might help you.

<a href="javascript:void(0);" onclick="selectItemByValue(document.getElementById('personlist'),11)">change</a>

function selectItemByValue(elmnt, value){

  for(var i=0; i < elmnt.options.length; i++)
  {
    if(elmnt.options[i].value === value) {
      elmnt.selectedIndex = i;
      break;
    }
  }
}

Your own answer technically wasn't incorrect, but you got the index wrong since indexes start at 0, not 1. That's why you got the wrong selection.

document.getElementById('personlist').getElementsByTagName('option')[**10**].selected = 'selected';

Also, your answer is actually a good one for cases where the tags aren't entirely English or numeric.

If they use, for example, Asian characters, the other solutions telling you to use .value() may not always function and will just not do anything. Selecting by tag is a good way to ignore the actual text and select by the element itself.

If you are adding the option with javascript

function AddNewOption(userRoutes, text, id) 
{
    var option = document.createElement("option");
    option.text = text;
    option.value = id;
    option.selected = "selected";
    userdRoutes.add(option);
}

An array Index will start from 0. If you want value=11 (Person1), you will get it with position getElementsByTagName('option')[10].selected.

mySelect.value = myValue;

Where mySelect is your selection box, and myValue is the value you want to change it to.

Tools as pure JavaScript code for handling Selectbox:

Graphical Understanding:

Image - A

Image - B

Image - C

Updated - 25-June-2019 | Fiddler DEMO

JavaScript Code:

/**
 * Empty Select Box
 * @param eid Element ID
 * @param value text
 * @param text text
 * @author Neeraj.Singh
 */
function emptySelectBoxById(eid, value, text) {
    document.getElementById(eid).innerHTML = "<option value='" + value + "'>" + text + "</option>";
}


/**
 * Reset Select Box
 * @param eid Element ID
 */

function resetSelectBoxById(eid) {
    document.getElementById(eid).options[0].selected = 'selected';
}


/**
 * Set Select Box Selection By Index
 * @param eid Element ID
 * @param eindx Element Index
 */

function setSelectBoxByIndex(eid, eindx) {
    document.getElementById(eid).getElementsByTagName('option')[eindx].selected = 'selected';
    //or
    document.getElementById(eid).options[eindx].selected = 'selected';
}


/**
 * Set Select Box Selection By Value
 * @param eid Element ID
 * @param eval Element Index
 */
function setSelectBoxByValue(eid, eval) {
    document.getElementById(eid).value = eval;
}


/**
 * Set Select Box Selection By Text
 * @param eid Element ID
 * @param eval Element Index
 */
function setSelectBoxByText(eid, etxt) {
    var eid = document.getElementById(eid);
    for (var i = 0; i < eid.options.length; ++i) {
        if (eid.options[i].text === etxt)
            eid.options[i].selected = true;
    }
}


/**
 * Get Select Box Text By ID
 * @param eid Element ID
 * @return string
 */

function getSelectBoxText(eid) {
    return document.getElementById(eid).options[document.getElementById(eid).selectedIndex].text;
}


/**
 * Get Select Box Value By ID
 * @param eid Element ID
 * @return string
 */

function getSelectBoxValue(id) {
    return document.getElementById(id).options[document.getElementById(id).selectedIndex].value;
}