How to programatically select an HTML option using JavaScript?

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;
}

mySelect.value = myValue;

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

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;
    }
  }
}

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

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

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

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);
}

You can use JQuery also

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

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.

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

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>

Note: Option Index count starts from 0. That means first option will be indexed at 0.

document.querySelector(".add__btn").addEventListener("click", function(){
  var index = 1; /*change option value here*/  document.querySelector(".add__type").options.selectedIndex = index;
  document.querySelector(".add__description").value = "Option Index";
  document.querySelector(".add__value").value = index;
});

<html>
    <div class="add__container">
         <select class="add__type">
            <option value="inc" selected>+</option>
            <option value="exp">-</option>
         </select>
         <input type="text" class="add__description" placeholder="Add description">
         <input type="number" class="add__value" placeholder="Value">
         <button class="add__btn"> Submit </button>
</div>

<h4> Default Option Value will be selected after pressing Submit </h4>

In case you are using mySelect.value = myOptionValue as per the accepted answer, but it still doesn't seem to work, then make sure that by the time you call your code the select options are fully rendered and interactive — if you are calling your code on page load, but it is not invoked via something like window.onload, DOMContentLoaded, qjuery's .ready() or whatever is used in your env then it is likely that you are running the code too early.

This will likely be the case when the select options are populated dynamically.

To check run the code manually via devtools when the page is fully loaded, or delay it with setTimeout() (use timeout for checking only, it's not a correct solution).

Jquery solution,

$('select').prop('selectedIndex', 1);