How do I programmatically set the value of a select box element using JavaScript?

Clear-cut explanation

For a broader understanding, let's dissect setting a select box value into comprehensible sections.

1. Selecting the box:

var selectBox = document.getElementById('selectBox'); // Or use querySelector
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2. Assigning the new value:

selectBox.value = 'optionValue';
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3. Alerting event listeners:

selectBox.dispatchEvent(new Event('change'));
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This three-step routine ensures a successful value assignment and dispatches a change event to update relevant event handlers.

Enhanced functionality

Apart from basic value setting, you may often need more intricate manipulations. Let's delve into them.

The jQuery way

If you're already using jQuery, the syntax simplifies remarkably:

$('#selectBox').val('optionValue').change(); // jQuery playing the magic flute!
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Dynamic content update

When working with options fetched from a server, or based on a user interaction, ensure the option exists before setting it:

// Does the option even exist? Let's check! 
if (document.querySelector('#selectBox option[value="optionValue"]')) {
    document.querySelector('#selectBox').value = 'optionValue'; // Safe to assign now.
}
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Cross-browser compatibility

Cross-browser compatibility is crucial. Verify your changes provide the same user experience across browsers.

Exception handling and prevention

Let's delve into a few sticky situations and discuss prevention methods.

Value mismatch

If you set a nonexistent value, it's as good as commanding the Saxophonist to play the flute. 🎷≠🎺

selectElement.value = 'flute'; // Uh-oh, no flute player in our orchestra!
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To avoid such facepalm moments, verify the option values.

Timing of dynamic load

Delay occurs when loading options via AJAX. Always assign values after rendering the new options:

// AJAX is slow! Let's wait for the band members to arrive.
loadOptions().then(() => {
    selectElement.value = 'piano';
});
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Event listener trigger

Remember that some event listeners might not detect programmatic changes. Send them an invite by dispatching an event:

var event = new Event('change', { bubbles: true });
selectElement.dispatchEvent(event); // Hey listen, we're changing the score!
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