Set selected value of dropdown in javascript

Question

If you are working with a web application, you may need to 'set the selected value of a dropdown in JavaScript'. This can be an effective way to customize the user experience of your website, allowing you to provide a more tailored experience for your visitors. In this article, we will look at how to set the selected value of a dropdown using JavaScript, as well as explore some potential use cases.

 Table of Contents:

1. Why is it important?
2. The Solutions
   1. Solution 1: Using the selectedIndex property
   2. Solution 2 Using a loop to go through the options 
   3. Solution 3: Using the value property
3. The Conclusion

Why is it important? #

JavaScript can be used to set the selected value of a dropdown list in order to make it easier for users to select the desired option.

This can be useful in situations where there are multiple options to choose from and the user is likely to make a mistake when selecting the correct option.

By using JavaScript to set the selected value, the user can be sure that the correct option has been chosen.

The Solutions #

Solution 1: Using the selectedIndex property #

The `selectedIndex` property is a numeric value that specifies the index of the selected option in a select list or dropdown menu.

It can be used to select an option from a list.

For example, if you have a dropdown in HTML like the following:

1
2
3

and you need for some reason to set the selected value to the second option whatever its value. 

start by selecting the dropdown then set its `selectedIndex` property like the following:

document.getElementById('numbers_dropdown').selectedIndex = 1;

The line of code selected the dropdown, then set its `selectedIndex` property to 1 which is the index number of the second option because the zero-based indexing, 

After running the code, the dropdown will show the second option value.

Solution 2: Loop through the options #

if you need to check the option value before you select it, then iterating through the options collection of the dropdown is the best method to check the values of the options and decide which one to set.

First, assign the dropdown to a variable, then iterate through its options to check the desired value and after that, assign the desired option selected attribute to true.

let's say we need to >set the selected value to number 3 in our dropdown, the code will be like the following:

var dropdown = document.getElementById("numbers_dropdown");
for (var i = 0; i < dropdown.options.length; i++) {
    if (dropdown.options[i].value === 3) {
        dropdown.options[i].selected = true;
        break;
    }
}

The break keyword here is useful because it gets out of the loop once we have found the desired value.

Solution 3: Assigning the value property #

You can assign the value property of the dropdown directly, but it has to be one of the options value attributes.

 In our example, I can assign the value property to 1, 2, and 3 but nothing other than those which are in the value attributes.

So if we need to get the first foption we need to assign the value property of the dropdown to the first option value attribute, like the following:

document.getElementById("numbers_dropdown").value = 1;

We can also do that with jQuery using the val() method, as the following:

$('#numbers_dropdown').val(1);

Check a brief introduction to jQuery here

Use Cases #

Case 1: Pre-selecting a value in a form

When a form is first displayed to a user, certain fields may need to be pre-populated with a default value.

For example, in a registration form, the country field may be pre-selected as the user's current country

Case 2: Updating a selected value based on user input

In some cases, the selected value of a dropdown may need to be updated based on user input.

For example, in an e-commerce website , the selected value of a dropdown may change to reflect the current category of products being viewed.

Case 3: Synchronizing multiple dropdowns

In certain situations, the option selected in one dropdown menu may need to be reflected in another dropdown menu.

For instance, in a flight booking website, the departure city selected in one dropdown may need to automatically be set as the arrival city in a different dropdown.

The Conclusion #

In conclusion, setting the selected value of a dropdown in JavaScript can be accomplished by utilizing the value property of the select element, along with the options collection and the selectedIndex property. By looping through the options and comparing the value property to the desired selection, the selected property can be set to true on the appropriate option. This technique can be useful for pre-selecting a value in a form or for dynamically updating the selection in response to user input.