JavaScript Required Explained: Form Validation, Modules (require vs import), and Required Parameters

By 佐川 直弘 | Naohiro Sagawa (運営者)

※記事内に広告を含みます。Amazonアソシエイトとして適格販売により収入を得ています。　

1. Introduction

JavaScript is one of the most widely used programming languages in web development. Within JavaScript, the concept of “required” plays an important role in areas such as form validation and module management. In this article, we’ll explain the features and usage related to “JavaScript required” with practical examples.

This article is intended for beginners who are just starting to learn JavaScript as well as intermediate learners who want to build more advanced, practical knowledge.

What You Will Learn in This Article

1. How to use and apply the required attribute in form validation
2. The differences between require and import in module management, and how to implement them
3. Practical examples of how to enforce required arguments in JavaScript functions

What Does “required” Mean in JavaScript?

“required” is a concept frequently used in both JavaScript and HTML. It is mainly used for the following two purposes.

1. Required input checks in forms

• By using the HTML required attribute, an error message is shown when a specific input field is left empty.

1. Declaring required dependencies in module management

• In environments such as Node.js, the require function is used to import external libraries and modules.

Why Is “required” Important?

“required” is essential for preventing user input mistakes and improving system stability. In form validation, it helps prevent invalid data from being submitted and ensures that only accurate information is received. In module management, it makes dependency management easier so you can use external libraries safely and reliably.

How to Read This Article

Each section introduces specific usage patterns with code examples. You’ll also find practical tips and FAQs, so you can quickly resolve questions as they come up.

2. The Basics and Practical Use of “required” in Form Validation

Form validation is an important process in web applications for verifying user input data. In JavaScript, you can achieve efficient input checks by using the HTML required attribute as well as dynamic validation through scripts. In this section, we’ll explain everything from the basics of the required attribute to practical, real-world examples.

2.1 What Is the HTML required Attribute?

Its Basic Role

The HTML required attribute is used to specify that input is mandatory for a particular form element. This allows the browser to validate the form before submission and prevent invalid input.

Basic Usage Example

Below is a simple example of the required attribute in HTML.

<form id="exampleForm">
  <label for="name">Name:</label>
  <input type="text" id="name" name="name" required>
  <button type="submit">Submit</button>
</form>

In this code, if the “Name” field is empty, the form will not be submitted and an error message will be displayed.

Notes

• The required attribute can only be applied to specific form elements such as input, select, and textarea.
• You can also customize the appearance of required fields using CSS.

input:required {
  border: 2px solid red;
}

2.2 Custom Validation Using JavaScript

If you need to check complex conditions that cannot be handled by the HTML required attribute alone, you can use JavaScript.

Example: Required Field Check with JavaScript

document.getElementById("exampleForm").addEventListener("submit", function(event) {
  const nameField = document.getElementById("name");
  if (!nameField.value) {
    alert("Name is required!");
    event.preventDefault(); // Prevent form submission
  }
});

In this script, if the name field is empty, an alert is shown and the form submission is canceled.

Checking Multiple Conditions

Here is an example that validates both the email format and whether the field is required at the same time.

document.getElementById("exampleForm").addEventListener("submit", function(event) {
  const emailField = document.getElementById("email");
  const emailPattern = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;

  if (!emailField.value || !emailPattern.test(emailField.value)) {
    alert("Please enter a valid email address.");
    event.preventDefault();
  }
});

2.3 Practical Example: Validation with Multiple Conditions

Requiring at Least One Checkbox Selection

In the following example, the user must select at least one checkbox.

document.getElementById("exampleForm").addEventListener("submit", function(event) {
  const checkboxes = document.querySelectorAll('input[name="options"]:checked');
  if (checkboxes.length === 0) {
    alert("Please select at least one option.");
    event.preventDefault();
  }
});

Requiring a Radio Button Selection

With radio buttons, you can ensure that exactly one option is selected.

document.getElementById("exampleForm").addEventListener("submit", function(event) {
  const radios = document.querySelectorAll('input[name="gender"]:checked');
  if (radios.length === 0) {
    alert("Please select a gender.");
    event.preventDefault();
  }
});

2.4 Summary

In this section, we introduced the basics of the HTML required attribute and examples of dynamic validation implemented with JavaScript. You should now understand that you can handle everything from simple required input checks to advanced validation based on multiple conditions.

3. “require” and “import” in Module Management

In JavaScript, module systems are used to improve code reusability and maintainability. In this section, we’ll take a detailed look at require and import, which are widely used for module management. Learn the differences and how to use each one so you can apply them appropriately depending on the situation.

3.1 Differences Between require and import

JavaScript module systems can be broadly divided into the following two types.

1. CommonJS Modules (require)

• This is the traditional module system primarily used in Node.js environments.
• It is commonly used in server-side JavaScript libraries and scripts.

1. ES Modules (import)

• This module system was introduced in ECMAScript 2015 (ES6).
• In front-end development, it is supported by modern browser versions and is recommended as a standardized format.

Comparison Table of Key Differences

3.2 How to Use require (CommonJS)

Basic Syntax

const moduleName = require('module-name');

Example: Loading the File System Module

const fs = require('fs');

fs.readFile('example.txt', 'utf8', (err, data) => {
  if (err) throw err;
  console.log(data);
});

In this example, you use Node.js’s built-in fs module to read the contents of a file.

Export Example

Module file math.js:

function add(a, b) {
  return a + b;
}

module.exports = add;

Importing from another file:

const add = require('./math');
console.log(add(2, 3)); // Output: 5

3.3 How to Use import (ES Modules)

Basic Syntax

import moduleName from 'module-name';

Example: Loading the File System Module

import { readFile } from 'fs/promises';

async function readExample() {
  const data = await readFile('example.txt', 'utf8');
  console.log(data);
}
readExample();

In this example, you use import along with an async function to read the contents of a file.

Export Example

Module file math.js:

export function add(a, b) {
  return a + b;
}

Importing from another file:

import { add } from './math.js';
console.log(add(2, 3)); // Output: 5

3.4 Notes and Troubleshooting

Be Careful When Mixing require and import

• require and import are generally not compatible, and mixing them can cause errors.
• If you use CommonJS, stick with require. If you use ES modules, stick with import.

Settings for Using ES Modules in Node.js

Modern Node.js supports ES modules, but you need the following configuration.

1. Use the .mjs extension, or add the following to package.json.

"type": "module"

2. Example of running a script that uses import:

node example.mjs

3.5 Summary

In this section, we explained the differences and usage of require and import in JavaScript module management systems.

• CommonJS (require): Used for server-side code and legacy codebases.
• ES Modules (import): Used as the standardized module system in modern browsers and Node.js.

By using them appropriately, you can build a more efficient development environment.

4. Implementing Required Argument Checks in Functions

In JavaScript, even if a function is called with missing arguments, it does not throw an error by default. Instead, missing values are treated as undefined. This flexibility can be convenient, but if important arguments are omitted, it may lead to bugs.

In this section, we’ll introduce methods to ensure that function arguments are required.

4.1 The Basic Idea Behind Required Argument Checks

JavaScript does not have a built-in feature to declare arguments as required. However, you can add custom code to check whether an argument exists and throw an error when it does not.

A Simple Example of a Required Check

function required(paramName) {
  throw new Error(`${paramName} is required`);
}

function greet(name = required('name')) {
  console.log(`Hello, ${name}!`);
}

greet(); // Error: name is required
greet('Alice'); // Output: Hello, Alice!

Explanation:

• The required function throws an error message to stop execution.
• The greet function uses the required function as a default value, which triggers an error if the argument is omitted.

4.2 Required Checks for Multiple Arguments

If there are multiple arguments, you need to validate each one individually.

Example: Multiple Argument Checks

function add(a = required('a'), b = required('b')) {
  return a + b;
}

console.log(add(2, 3)); // Output: 5
console.log(add(2)); // Error: b is required

Key Points:

• By setting default values for each argument, you can throw an error when an argument is omitted.
• This allows you to stop execution when required parameters are missing.

4.3 Required Checks Using Objects

When you accept an object as an argument, you can check whether required properties exist.

Example: Validating Object Arguments

function createUser({ name = required('name'), age = required('age') }) {
  return { name, age };
}

console.log(createUser({ name: 'Alice', age: 25 })); // Output: { name: 'Alice', age: 25 }
console.log(createUser({ name: 'Bob' })); // Error: age is required

Explanation:

• For each property in the object argument, the required function is also set as a default value.
• This makes the structure of input data clearer and improves maintainability.

4.4 Advanced Validation: Type Checks and Conditional Validation

Example Combining Type Checks

function processData(data = required('data')) {
  if (typeof data !== 'string') {
    throw new Error('data must be a string');
  }
  console.log(data.toUpperCase());
}

processData('hello'); // Output: HELLO
processData(123); // Error: data must be a string

Key Points:

• This checks not only whether the argument is provided, but also whether it has the correct type.
• Throwing an error for invalid types enables stricter validation.

4.5 Troubleshooting and Debugging

1. Improve the Error Message When an Error Occurs

Including the function name and the expected argument name in your error message makes it easier to identify the issue.

Example:

function required(paramName) {
  throw new Error(`Missing required parameter: ${paramName}`);
}

2. Add Data Validation Before Execution

If you receive data from forms or APIs, validate the data format before calling the function so you can fix issues in advance.

4.6 Summary

In this section, we explained how to implement required argument checks in JavaScript functions.

Summary of Key Points

1. Use default values to throw an error when required arguments are missing.
2. Validate object argument properties as well to support flexible validation.
3. Combine type checks and conditional validation to implement stricter checks.

By applying these techniques, you can improve the safety and reliability of your code.

5. Summary

In this article, we covered “JavaScript required” with a focus on form validation, module management, and how to implement required checks in functions. Here, we’ll review the key points from each section and organize the overall takeaways.

5.1 The required Attribute in Form Validation

Key Basics

• The HTML required attribute allows you to mark specific input fields as mandatory.
• By using JavaScript, you can implement more flexible and advanced validation.

Practical Examples Covered

• We explained custom validation for requiring checkbox and radio button selections.
• Multiple-condition checks (such as email format and numeric validation) can also be handled using JavaScript.

This helps prevent input mistakes while improving the user experience.

5.2 require and import in Module Management

Differences and How to Choose

• require (CommonJS): Mainly used in server-side Node.js environments and supports synchronous module loading.
• import (ES Modules): An asynchronous module system used in browsers and modern Node.js environments, recommended for modern JavaScript development.

Real-World Usage Examples

• We demonstrated practical examples using the file system module.
• We also covered troubleshooting and how to handle compatibility issues, providing actionable solutions for real development scenarios.

Using these approaches makes code management more efficient and maintainable.

5.3 Required Argument Checks in Functions

From Simple Implementations to Practical Use Cases

• We introduced examples that use default arguments and custom error handling to throw errors when arguments are omitted.

Advanced Validation Tips

• By combining object argument validation and type checks, you can implement stricter and more reliable validation.

This helps prevent unexpected behavior and bugs while improving reliability and scalability.

5.4 Key Takeaways from the Entire Article

1. Form Validation

• Combine simple HTML attributes with dynamic JavaScript validation to achieve flexible validation.

2. Module Management

• Understand how to choose between CommonJS and ES Modules depending on your environment, and implement module management effectively.

3. Required Checks

• Use custom required-check functions and type validation to write safer, easier-to-maintain code.

5.5 Next Steps

Use what you learned in this article and move on to the following steps.

1. Apply It to Real Projects: Try implementing form validation and module management in your own projects.
2. Continue Learning Advanced JavaScript:

• Validation during API communication
• Data management using asynchronous processing
• Code verification using testing frameworks

1. Keep Updating Your Skills: JavaScript is constantly evolving. By learning the latest features and continuously improving your code, you can build more advanced skills.

6. FAQ (Frequently Asked Questions)

In this section, we’ll introduce common questions and solutions related to “JavaScript required.” We’ll also include practical troubleshooting examples and important notes to support hands-on learning and real-world debugging.

Q1: Why doesn’t the HTML required attribute work?

A1: Common Causes and Solutions

Cause 1: The form has the novalidate attribute.

• If novalidate is set, the browser skips HTML validation.

Solution:

<form novalidate>
  <input type="text" required>
</form>

Remove novalidate from this code and check whether it works correctly.

Cause 2: JavaScript is controlling form submission.

• If you manually control form submission using JavaScript, HTML validation may be ignored.

Solution:

const form = document.getElementById("myForm");
form.addEventListener("submit", function (event) {
  if (!form.checkValidity()) {
    alert("There are input errors!");
    event.preventDefault();
  }
});

Q2: Can I use require and import in the same codebase?

A2: Generally Not Recommended

require is syntax used in the CommonJS module system and has been available since early versions of Node.js. On the other hand, import is ES module syntax used in modern JavaScript environments.

Problems with Mixing Them

• require and import are not compatible. Mixing them can cause errors.

Solution:

Use one module system consistently across your project.

CommonJS example:

const fs = require('fs');

ES module example:

import { readFile } from 'fs/promises';

Q3: Can I customize the error message for required argument checks in functions?

A3: Yes, you can.

Example: Customizing the Error Message

function required(paramName) {
  throw new Error(`The parameter "${paramName}" is required.`);
}

function greet(name = required('name')) {
  console.log(`Hello, ${name}!`);
}

greet(); // Error: The parameter "name" is required.

Q4: Can I validate multiple conditions at the same time in form validation?

A4: Yes, with JavaScript.

Example: Required input + minimum length check

document.getElementById("form").addEventListener("submit", function(event) {
  const username = document.getElementById("username");
  if (!username.value || username.value.length < 3) {
    alert("Please enter a username with at least 3 characters.");
    event.preventDefault();
  }
});

Q5: Can I dynamically add or remove the required attribute with JavaScript?

A5: Yes, you can.

Example: Dynamically adding/removing required

const input = document.getElementById('dynamicInput');

// Make it required
input.setAttribute('required', true);

// Remove the required constraint
input.removeAttribute('required');

Q6: Are there any precautions when using ES modules?

A6: Key Points to Watch Out For

1. File extension:

• When using ES modules, use the .mjs extension or add the following setting to package.json.

"type": "module"

2. Asynchronous loading:

• ES modules are loaded asynchronously, so be careful when combining them with synchronous processing.

3. Browser compatibility:

• Modern browsers generally support ES modules, but older browsers may not. In that case, use a transpiler such as Babel.

6.7 Summary

In this FAQ section, we introduced common questions and solutions related to “JavaScript required,” with practical examples.

Main Takeaways:

1. We explained why the HTML required attribute may not work and how to fix it.
2. We clarified the differences and usage of require and import in module management.
3. We provided examples of custom error messages and dynamic form validation using JavaScript.

Use this article as a reference to apply “JavaScript required” effectively in a wide range of scenarios and build more efficient development workflows.