How to check data type in HTML

How to check data type in HTML

HTML is a markup language that is used to create web pages. HTML elements can have different types of attributes that store additional information about the element. For example, an

<input>

Sometimes, we may need to check the data type of an HTML attribute or element for various purposes, such as validating user input, performing calculations, or manipulating the DOM. In this article, we will learn how to check the data type in HTML using different methods and tools.

Using HTML5 functionality

HTML5 provides some built-in functionality to help validate and check the data type of HTML attributes and elements. Here are some common cases:

• Making fields required using required

  : This attribute indicates that the user must fill in the input before submitting the form. For example, <input type="text" name="name" required> will not allow the form to be submitted unless the user enters some text in the name field.

• Constraining the length of data using minlength, maxlength: These attributes specify the minimum and maximum number of characters that the user can enter in a text input. For example,

  <input type="text" name="username" minlength="4" maxlength="10"> will only accept usernames between 4 and 10 characters long.

• Restricting the type of data using type: This attribute specifies what kind of data the input accepts, such as text, number, email, date, etc. For example,

  <input type="email" name="email">

  will only accept valid email addresses as input.
• Specifying data patterns using pattern

  : This attribute specifies a regular expression that the input value must match. For example, <input type="text" name="phone" pattern="\d{3}-\d{3}-\d{4}">

  will only accept phone numbers in the format xxx-xxx-xxxx.

When the input value matches the above HTML5 validation, it gets assigned a pseudo-class :valid, and :invalid if it doesn’t. We can use CSS to style the valid and invalid inputs differently. For example:

input:valid {
  border: 2px solid green;
}

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

Using JavaScript

JavaScript is a scripting language that can interact with HTML elements and attributes. We can use JavaScript to check the data type of HTML attributes and elements in various ways. Here are some examples:

• Using typeof: This operator returns a string that indicates the type of the operand. For example, typeof 42 returns "number", and typeof "hello" returns "string". We can use this operator to check the type of an HTML attribute or element by accessing its value property. For example:

var input = document.getElementById("txtinp"); // get the input element by id
var type = typeof input.value; // get the type of its value
console.log(type); // print the type

• Using instanceof: This operator returns a boolean value that indicates whether an object is an instance of a specific constructor or class. For example, [1, 2, 3] instanceof Array returns true, and "hello" instanceof String returns false. We can use this operator to check if an HTML element is an instance of a specific HTML class. For example:

var div = document.getElementById("mydiv"); // get the div element by id
var isDiv = div instanceof HTMLDivElement; // check if it is an instance of HTMLDivElement
console.log(isDiv); // print the result

• Using custom functions: We can also write our own functions to check the data type of an HTML attribute or element based on some criteria or logic. For example, we can write a function that checks if an input element is a checkbox or not:

function isCheckbox(input) {
  return input.type === "checkbox"; // return true if the input type is checkbox
}

var checkbox = document.getElementById("mycheckbox"); // get the checkbox element by id
var result = isCheckbox(checkbox); // check if it is a checkbox
console.log(result); // print the result

Conclusion

In this article, we learned how to check the data type in HTML using different methods and tools. We saw how to use HTML5 functionality, JavaScript operators, and custom functions to validate and check the data type of HTML attributes and elements. We also learned how to use CSS pseudo-classes to style valid and invalid inputs differently. Checking the data type in HTML is useful for various purposes, such as ensuring data quality, performing calculations, or manipulating the DOM.