Cara menggunakan javascript get return value

A web form has a client-server relationship. They are used to send data handled by a web server for processing and storage. The form itself is the client, and the server is any storage mechanism that can be used to store, retrieve and send data when needed.

This guide will teach you how to create a web form with Next.js.

HTML forms are built using the

tag. It takes a set of attributes and fields to structure the form for features like text fields, checkboxes, dropdown menus, buttons, radio buttons, etc.

Here's the syntax of an HTML form:

The front-end looks like this:

The HTML tag acts as a container for different elements like text field and submit button. Let's study each of these elements:

• action: An attribute that specifies where the form data is sent when the form is submitted. It's generally a URL (an absolute URL or a relative URL).
• Password: Submit 0: Specifies the HTTP method, i.e., Password: Submit 1 or Password: Submit 2 used to send data while submitting the form.
• : An element that defines the label for other form elements. Labels aid accessibility, especially for screen readers.
• : The form element that is widely used to structure the form fields. It depends significantly on the value of the Password: Submit 5 attribute. Input types can be text, Password: Submit 7, Password: Submit 8, Password: Submit 9, and more.
• : Represents a clickable button that's used to submit the form data.

A process that checks if the information provided by a user is correct or not. Form validation also ensures that the provided information is in the correct format (e.g. there's an @ in the email field). These are of two types:

• Client-side: Validation is done in the browser
• Server-side: Validation is done on the server

Though both of these types are equally important, this guide will focus on client-side validation only.

Client-side validation is further categorized as:

• Built-in: Uses HTML-based attributes like npx create-next-app 0, Password: Submit 5, npx create-next-app 2, npx create-next-app 3, npx create-next-app 4, etc.
• JavaScript-based: Validation that's coded with JavaScript.

• npx create-next-app 0: Specifies which fields must be filled before submitting the form.
• Password: Submit 5: Specifies the data's type (i.e a number, email address, string, etc).
• npx create-next-app 2: Specifies minimum length for the text data string.
• npx create-next-app 3: Specifies maximum length for the text data string.

So, a form using this attributes may look like:

With these validation checks in place, when a user tries to submit an empty field for Name, it gives an error that pops right in the form field. Similarly, a roll number can only be entered if it's 10-20 characters long.

Form Validation is important to ensure that a user has submitted the correct data, in a correct format. JavaScript offers an additional level of validation along with HTML native form attributes on the client side. Developers generally prefer validating form data through JavaScript because its data processing is faster when compared to server-side validation, however front-end validation may be less secure in some scenarios as a malicious user could always send malformed data to your server.

The following example shows using JavaScript to validate a form:

Roll Number: Name: Submit

The HTML script tag is used to embed any client-side JavaScript. It can either contain inline scripting statements (as shown in the example above) or point to an external script file via the npx create-next-app 9 attribute. This example validates the name and roll number of a user. The First name: Last name: Submit 0 function does not allow an empty name field, and the roll number must be at least three digits long. The validation is performed when you hit the Submit button. You are not redirected to the next page until the given values are correct.

JavaScript validation with Regular Expressions uses the npx create-next-app 4 HTML attribute. A regular expression (commonly known as RegEx) is an object that describes a pattern of characters. You can only apply the npx create-next-app 4 attribute to the element. This way, you can validate the input value using Regular Expressions (RegEx) by defining your own rules. Once again, if the value does not match the defined pattern, the input will give an error. The below example shows using the npx create-next-app 4 attribute on an First name: Last name: Submit 5 element:

Password: Submit

The password form field must only contain digits (0 to 9), lowercase alphabets (a to z) and it must be no more than 15 characters in length. No other characters (#,$,&, etc.) are allowed. The rule in RegEx is written as First name: Last name: Submit 6.

To learn more about HTML forms, check out the MDN Web Docs.

In the following section you will be creating forms in React using Next.js.

Create a new Next.js app. You can use the for a quick start. In your command line terminal, run the following:

npx create-next-app

Answer the questions to create your project, and give it a name, this example uses First name: Last name: Submit 7. Next First name: Last name: Submit 8 into this directory, and run First name: Last name: Submit 9 or export default function Form() { return ( First Name Last Name Submit ) } 0 command to start the development server.

Open the URL printed in the terminal to ensure that your app is running successfully.

Both the client and the server will be built using Next.js. For the server part, create an API endpoint where you will send the form data.

Next.js offers a file-based system for routing that's built on the concept of pages. Any file inside the folder export default function Form() { return ( First Name Last Name Submit ) } 1 is mapped to export default function Form() { return ( First Name Last Name Submit ) } 2 and will be treated as an API endpoint instead of a page. This API endpoint is going to be server-side only.

Go to export default function Form() { return ( First Name Last Name Submit ) } 1, create a file called export default function Form() { return ( First Name Last Name Submit ) } 4 and paste this code written in Node.js:

This form export default function Form() { return ( First Name Last Name Submit ) } 5 function will receive the request export default function Form() { return ( First Name Last Name Submit ) } 6 from the client (i.e. submitted form data). And in return, it'll send a response export default function Form() { return ( First Name Last Name Submit ) } 7 as JSON that will have both the first and the last name. You can access this API endpoint at export default function Form() { return ( First Name Last Name Submit ) } 8 or replace the localhost URL with an actual Vercel deployment when you deploy.

Moreover, you can also attach this API to a database like MongoDB or Google Sheets. This way, your submitted form data will be securely stored for later use. For this guide, no database is used. Instead, the same data is returned to the user to demo how it's done.

You can now use export default function Form() { return ( First Name Last Name Submit ) } 9 relative endpoint inside the action attribute of the form. You are sending form data to the server when the form is submitted via Password: Submit 2 HTTP method (which is used to send data).

First name: Last name: Submit

If you submit this form, it will submit the data to the forms API endpoint export default function Form() { return ( First Name Last Name Submit ) } 9. The server then responds, generally handling the data and loading the URL defined by the action attribute, causing a new page load. So in this case you'll be redirected to export default function Form() { return ( First Name Last Name Submit ) } 8 with the following response from the server.

You have created a Next.js API Route for form submission. Now it's time to configure the client (the form itself) inside Next.js using React. The first step will be extending your knowledge of HTML forms and converting it into React (using JSX).

Here's the same form in a React function component written using JSX.

export default function Form() { return ( First Name Last Name Submit ) }

Here's what changed:

• The export default function PageWithoutJSbasedForm() { return ( First Name Last Name Submit ) } 4 attribute is changed to export default function PageWithoutJSbasedForm() { return ( First Name Last Name Submit ) } 5. (Since export default function PageWithoutJSbasedForm() { return ( First Name Last Name Submit ) } 4 is a keyword associated with the "for" loop in JavaScript, React elements use export default function PageWithoutJSbasedForm() { return ( First Name Last Name Submit ) } 5 instead.)
• The action attribute now has a relative URL which is the form API endpoint.

This completes the basic structure of your Next.js-based form.

You can view the entire source code of next-forms example repo that we're creating here as a working example. Feel free to clone it and start right away. This demo is built with create-next-app, and you can preview the basic form CSS styles inside export default function PageWithoutJSbasedForm() { return ( First Name Last Name Submit ) } 9 file.

JavaScript brings interactivity to our web applications, but sometimes you need to control the JavaScript bundle from being too large, or your sites visitors might have JavaScript disabled.

There are several reasons why users disable JavaScript:

• Addressing bandwidth constraints
• Increasing device (phone or laptop) battery life
• For privacy so they won’t be tracked with analytical scripts

Regardless of the reason, disabling JavaScript will impact site functionality partially, if not completely.

Next open the First name: Last name: Submit 7 directory. Inside the 1 directory, create a file 2.

Quick Tip: In Next.js, a page is a React Component exported from a 3, 4, 5, or 6 file in the pages directory. Each page is associated with a route based on its file name.

Example: If you create 7, it will be accessible at 8.

Let's use the same code from above:

export default function PageWithoutJSbasedForm() { return ( First Name Last Name Submit ) }

With JavaScript disabled, when you hit the Submit button, an event is triggered, which collects the form data and sends it to our forms API endpoint as defined in the action attribute and using Password: Submit 2 HTTP Password: Submit 0. You'll be redirected to the export default function Form() { return ( First Name Last Name Submit ) } 9 endpoint since that's how form action works.

The form data will be submitted on the server as a request export default function Form() { return ( First Name Last Name Submit ) } 6 to the form handler function written above. It will process the data and return a JSON string as a response export default function Form() { return ( First Name Last Name Submit ) } 7 with your submitted name included.

To improve the experience here, as a response you can redirect the user to a page and thank them for submitting the form.

Inside 1, you'll create another file called text7. This will create a text8 page on your Next.js app.

Now, as soon as the form is submitted, we prevent the form's default behavior of reloading the page. We'll take the form data, convert it to JSON string, and send it to our server, the API endpoint. Finally, our server will respond with the name submitted. All of this with a basic JavaScript text9 function.