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>
![Option gets Attribute selected by using defaultSelected]()
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.
