Html form hidden javascript value

Note: The input and change events do not apply to this input type. Hidden inputs cannot be focused even using JavaScript (e.g. hiddenInput.focus() ).

Value

The element’s value attribute holds a string that contains the hidden data you want to include when the form is submitted to the server. This specifically can’t be edited or seen by the user via the user interface, although you could edit the value via browser developer tools.

Warning: While the value isn’t displayed to the user in the page’s content, it is visible—and can be edited—using any browser’s developer tools or «View Source» functionality. Do not rely on hidden inputs as a form of security.

Additional attributes

name

This is actually one of the common attributes, but it has a special meaning available for hidden inputs. Normally, the name attribute functions on hidden inputs just like on any other input. However, when the form is submitted, a hidden input whose name is set to _charset_ will automatically be reported with the value set to the character encoding used to submit the form.

Using hidden inputs

As mentioned above, hidden inputs can be used anywhere that you want to include data the user can’t see or edit along with the form when it’s submitted to the server. Let’s look at some examples that illustrate its use.

Tracking edited content

One of the most common uses for hidden inputs is to keep track of what database record needs to be updated when an edit form is submitted. A typical workflow looks like this:

User decides to edit some content they have control over, such as a blog post, or a product entry. They get started by pressing the edit button.
The content to be edited is taken from the database and loaded into an HTML form to allow the user to make changes.
After editing, the user submits the form, and the updated data is sent back to the server to be updated in the database.

The idea here is that during step 2, the ID of the record being updated is kept in a hidden input. When the form is submitted in step 3, the ID is automatically sent back to the server with the record content. The ID lets the site’s server-side component know exactly which record needs to be updated with the submitted data.

You can see a full example of what this might look like in the Examples section below.

Improving website security

Hidden inputs are also used to store and submit security tokens or secrets, for the purposes of improving website security. The basic idea is that if a user is filling in a sensitive form, such as a form on their banking website to transfer some money to another account, the secret they would be provided with would prove that they are who they say they are, and that they are using the correct form to submit the transfer request.

This would stop a malicious user from creating a fake form, pretending to be a bank, and emailing the form to unsuspecting users to trick them into transferring money to the wrong place. This kind of attack is called a Cross Site Request Forgery (CSRF); pretty much any reputable server-side framework uses hidden secrets to prevent such attacks.

Note: Placing the secret in a hidden input doesn’t inherently make it secure. The key’s composition and encoding would do that. The value of the hidden input is that it keeps the secret associated with the data and automatically includes it when the form is sent to the server. You need to use well-designed secrets to actually secure your website.

Validation

Hidden inputs don’t participate in constraint validation; they have no real value to be constrained.

Examples

Let’s look at how we might implement a simple version of the edit form we described earlier (see Tracking edited content), using a hidden input to remember the ID of the record being edited.

The edit form’s HTML might look a bit like this:

form> div> label for="title">Post title:label> input type="text" id="title" name="title" value="My excellent blog post" /> div> div> label for="content">Post content:label> textarea id="content" name="content" cols="60" rows="5"> This is the content of my excellent blog post. I hope you enjoy it! textarea> div> div> button type="submit">Update postbutton> div> input type="hidden" id="postId" name="postId" value="34657" /> form>

Let’s also add some simple CSS:

html  font-family: sans-serif; > form  width: 500px; > div  display: flex; margin-bottom: 10px; > label  flex: 2; line-height: 2; text-align: right; padding-right: 20px; > input, textarea  flex: 7; font-family: sans-serif; font-size: 1.1rem; padding: 5px; > textarea  height: 60px; >

The server would set the value of the hidden input with the ID » postID » to the ID of the post in its database before sending the form to the user’s browser and would use that information when the form is returned to know which database record to update with modified information. No scripting is needed in the content to handle this.

The output looks like this:

Note: You can also find the example on GitHub (see the source code, and also see it running live).

When submitted, the form data sent to the server will look something like this:

Even though the hidden input cannot be seen at all, its data is still submitted.

Technical summary

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Input Hidden value Property

Get the value of the value attribute of a hidden input field:

Description

The value property sets or returns the value of the value attribute of the hidden input field.

The value attribute defines the default value of the hidden input field.

Browser Support

Syntax

Return the value property:

Property Values

Technical Details

More Examples

Example

Change the value of the hidden field:

Example

Submitting a form — How to change the value of the hidden field:

document.getElementById(«myInput»).value = «USA»;
document.getElementById(«demo»).innerHTML = «The value of the value attribute was changed. Try to submit the form again.»;

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Set Hidden Field Value In JavaScript

We can set a hidden field value in a form in JavaScript by changing the type property of the field with the help of the getElementById() method.

document.getElementById("someField").type = "hidden";

The above code would change the property type to hidden.

Let’s take a look at an example below:

Let’s say we have the following HTML form:

As you can see in the code above, we have two simple text input fields.

If we wanted to hide the input field for Full Name, we would use the following JavaScript code:

document.getElementById("fname").type = "hidden";

It can be very useful to hide form fields from the user. Just note that when a form field has the type of hidden, it will not be able to be seen on the webpage by the user. However, the user could still access the information in the hidden field with the use of a browser inspector that most browsers have. So you should make sure not to store any data in the hidden field that you do not want someone to have access to.

Example of Setting an Input Field Value to Hidden In JavaScript

In this simple example, we will just have a standard HTML form. We will provide the HTML code for it and let the user enter a name and submit the form. The form will not have any backend connected to it, so when you submit the form, it should just refresh the page and put the name variable you entered in the URL.

 What is Your Name?

The form you will see will only show a name field, its label, and a submit button. But there is also a hidden email field. We have added JavaScript code to this page to hide the field right away.

Here is that JavaScript code:

document.getElementById("email").type = "hidden";

Here is the form for you to see with the hidden email field:

And here is the Full Code and JavaScript:

 What is Your Name?

Hopefully this article has been useful for you to understand how to set a hidden field value in JavaScript.

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Html form hidden javascript value