set option “selected” attribute from dynamic created option

Question

I have a dynamically created select option using a javascript function. the select object is

<         


        

Answer 1

What you want to do is set the selectedIndex attribute of the select box.

country.options.selectedIndex = index_of_indonesia;

Changing the 'selected' attribute will generally not work in IE. If you really want the behavior you're describing, I suggest you write a custom javascript reset function to reset all the other values in the form to their default.

Answer 2

So many wrong answers!

To specify the value that a form field should revert to upon resetting the form, use the following properties:

• Checkbox or radio button: defaultChecked
• Any other <input> control: defaultValue
• Option in a drop down list: defaultSelected

So, to specify the currently selected option as the default:

var country = document.getElementById("country");
country.options[country.selectedIndex].defaultSelected = true;

It may be a good idea to set the defaultSelected value for every option, in case one had previously been set:

var country = document.getElementById("country");
for (var i = 0; i < country.options.length; i++) {
    country.options[i].defaultSelected = i == country.selectedIndex;
}

Now, when the form is reset, the selected option will be the one you specified.

Answer 3

You're overthinking it:

var country = document.getElementById("country");
country.options[country.options.selectedIndex].selected = true;

Answer 4

// get the OPTION we want selected
var $option = $('#SelectList').children('option[value="'+ id +'"]');
// and now set the option we want selected
$option.attr('selected', true);​​

Answer 5

Make option defaultSelected

HTMLOptionElement.defaultSelected = true;     // JS
$('selector').prop({defaultSelected: true});  // jQuery  

HTMLOptionElement MDN

If the SELECT element is already added to the document (statically or dynamically), to set an option to Attribute-selected and to make it survive a HTMLFormElement.reset() - defaultSelected is used:

const EL_country = document.querySelector('#country');
EL_country.value = 'ID';   // Set SELECT value to 'ID' ("Indonesia")
EL_country.options[EL_country.selectedIndex].defaultSelected = true; // Add Attribute selected to Option Element

document.forms[0].reset(); // "Indonesia" is still selected

<form>
  <select name="country" id="country">
    <option value="AF">Afghanistan</option>
    <option value="AL">Albania</option>
    <option value="HR">Croatia</option>
    <option value="ID">Indonesia</option>
    <option value="ZW">Zimbabwe</option>
  </select>
</form>

The above will also work if you build the options dynamically, and than (only afterwards) you want to set one option to be defaultSelected.

const countries = {
  AF: 'Afghanistan',
  AL: 'Albania',
  HR: 'Croatia',
  ID: 'Indonesia',
  ZW: 'Zimbabwe',
};

const EL_country = document.querySelector('#country');

// (Bad example. Ideally use .createDocumentFragment() and .appendChild() methods)
EL_country.innerHTML = Object.keys(countries).reduce((str, key) => str += `<option value="${key}">${countries[key]}</option>`, ''); 

EL_country.value = 'ID';
EL_country.options[EL_country.selectedIndex].defaultSelected = true;

document.forms[0].reset(); // "Indonesia" is still selected

<form>
  <select name="country" id="country"></select>
</form>

Make option defaultSelected while dynamically creating options

To make an option selected while populating the SELECT Element, use the Option() constructor MDN

var optionElementReference = new Option(text, value, defaultSelected, selected);

const countries = {
  AF: 'Afghanistan',
  AL: 'Albania',
  HR: 'Croatia',
  ID: 'Indonesia',     // <<< make this one defaultSelected
  ZW: 'Zimbabwe',
};

const EL_country = document.querySelector('#country');
const DF_options = document.createDocumentFragment();

Object.keys(countries).forEach(key => {
  const isIndonesia = key === 'ID';  // Boolean
  DF_options.appendChild(new Option(countries[key], key, isIndonesia, isIndonesia))
});

EL_country.appendChild(DF_options);

document.forms[0].reset(); // "Indonesia" is still selected

<form>
  <select name="country" id="country"></select>
</form>

In the demo above Document.createDocumentFragment is used to prevent rendering elements inside the DOM in a loop. Instead, the fragment (containing all the Options) is appended to the Select only once.

---

SELECT.value vs. OPTION.setAttribute vs. OPTION.selected vs. OPTION.defaultSelected

Although some (older) browsers interpret the OPTION's selected attribute as a "string" state, the WHATWG HTML Specifications html.spec.whatwg.org state that it should represent a Boolean selectedness

The selectedness of an option element is a boolean state, initially false. Except where otherwise specified, when the element is created, its selectedness must be set to true if the element has a selected attribute.
html.spec.whatwg.org - Option selectedness

one can correctly deduce that just the name selected in <option value="foo" selected> is enough to set a truthy state.

---

Comparison test of the different methods

const EL_select = document.querySelector('#country');
const TPL_options = `
  <option value="AF">Afghanistan</option>
  <option value="AL">Albania</option>
  <option value="HR">Croatia</option>
  <option value="ID">Indonesia</option>
  <option value="ZW">Zimbabwe</option>
`;

// https://developer.mozilla.org/en-US/docs/Web/API/MutationObserver/MutationObserver
const mutationCB = (mutationsList, observer) => {
  mutationsList.forEach(mu => {
    const EL = mu.target;
    if (mu.type === 'attributes') {
      return console.log(`* Attribute ${mu.attributeName} Mutation. ${EL.value}(${EL.text})`);
    }
  });
};

// (PREPARE SOME TEST FUNCTIONS)

const testOptionsSelectedByProperty = () => {
  const test = 'OPTION with Property selected:';
  try {
    const EL = [...EL_select.options].find(opt => opt.selected);
    console.log(`${test} ${EL.value}(${EL.text}) PropSelectedValue: ${EL.selected}`);
  } catch (e) {
    console.log(`${test} NOT FOUND!`);
  }
} 

const testOptionsSelectedByAttribute = () => {
  const test = 'OPTION with Attribute selected:'
  try {
    const EL = [...EL_select.options].find(opt => opt.hasAttribute('selected'));
    console.log(`${test} ${EL.value}(${EL.text}) AttrSelectedValue: ${EL.getAttribute('selected')}`);
  } catch (e) {
    console.log(`${test} NOT FOUND!`);
  }
} 

const testSelect = () => {
  console.log(`SELECT value:${EL_select.value} selectedIndex:${EL_select.selectedIndex}`);
}

const formReset = () => {
  EL_select.value = '';
  EL_select.innerHTML = TPL_options;
  // Attach MutationObserver to every Option to track if Attribute will change
  [...EL_select.options].forEach(EL_option => {
    const observer = new MutationObserver(mutationCB);
    observer.observe(EL_option, {attributes: true});
  });
}

// -----------
// LET'S TEST! 

console.log('\n1. Set SELECT value');
formReset();
EL_select.value = 'AL'; // Constatation: MutationObserver did NOT triggered!!!!
testOptionsSelectedByProperty();
testOptionsSelectedByAttribute();
testSelect();

console.log('\n2. Set HTMLElement.setAttribute()');
formReset();
EL_select.options[2].setAttribute('selected', true); // MutationObserver triggers
testOptionsSelectedByProperty();
testOptionsSelectedByAttribute();
testSelect();

console.log('\n3. Set HTMLOptionElement.defaultSelected');
formReset();
EL_select.options[3].defaultSelected = true; // MutationObserver triggers
testOptionsSelectedByProperty();
testOptionsSelectedByAttribute();
testSelect();

console.log('\n4. Set SELECT value and HTMLOptionElement.defaultSelected');
formReset();
EL_select.value = 'ZW'
EL_select.options[EL_select.selectedIndex].defaultSelected = true; // MutationObserver triggers
testOptionsSelectedByProperty();
testOptionsSelectedByAttribute();
testSelect();

/* END */
console.log('\n*. Getting MutationObservers out from call-stack...');

<form>
  <select name="country" id="country"></select>
</form>

Although the test 2. using .setAttribute() seems at first the best solution since both the Element Property and Attribute are unison, it can lead to confusion, specially because .setAttribute expects two parameters:

EL_select.options[1].setAttribute('selected', false);
// <option value="AL" selected="false"> // But still selected!

will actually make the option selected

Should one use .removeAttribute() or perhaps .setAttribute('selected', ???) to another value? Or should one read the state by using .getAttribute('selected') or by using .hasAttribute('selected')?

Instead test 3. (and 4.) using defaultSelected gives the expected results:

• Attribute selected as a named Selectedness state.
• Property selected on the Element Object, with a Boolean value.

Answer 6

Instead of modifying the HTML itself, you should just set the value you want from the relative option element:

$(function() {
    $("#country").val("ID");
});

In this case "ID" is the value of the option "Indonesia"