HTML
HTML Introduction:
What is HTML?
- HTML stands for Hyper Text Markup Language
- HTML is the standard markup language for creating Web pages
- HTML describes the structure of a Web page
- HTML consists of a series of elements
- HTML elements tell the browser how to display the content
- HTML elements label pieces of content such as "this is a heading", "this is a paragraph", "this is a link", etc.
A Simple HTML Document:
<head>
<title>Page Title</title>
</head>
<body>
<h1>My First Heading</h1>
<p>My first paragraph.</p>
</body>
</html>
Example Explained
- The
<!DOCTYPE html>declaration defines that this document is an HTML5 document - The
<html>element is the root element of an HTML page - The
<head>element contains meta information about the HTML page - The
<title>element specifies a title for the HTML page (which is shown in the browser's title bar or in the page's tab) - The
<body>element defines the document's body, and is a container for all the visible contents, such as headings, paragraphs, images, hyperlinks, tables, lists, etc. - The
<h1>element defines a large heading - The
<p>element defines a paragraph
What is an HTML Element?
An HTML element is defined by a start tag, some content, and an end tag:
The HTML element is everything from the start tag to the end tag:
| Start tag | Element content | End tag |
|---|---|---|
| <h1> | My First Heading | </h1> |
| <p> | My first paragraph. | </p> |
| <br> | none | none |
HTML Page Structure:
Below is a visualization of an HTML page structure:
HTML Documents
All HTML documents must start with a document type declaration: <!DOCTYPE html>.
The HTML document itself begins with <html> and ends with </html>.
The visible part of the HTML document is between <body> and </body>.
The <!DOCTYPE> Declaration
The <!DOCTYPE> declaration represents the document type, and helps browsers to display web pages correctly.
It must only appear once, at the top of the page (before any HTML tags).
The <!DOCTYPE> declaration is not case sensitive.
The <!DOCTYPE> declaration for HTML5 is:
HTML Headings
HTML headings are defined with the <h1> to <h6> tags.
<h1> defines the most important heading. <h6> defines the least important heading:
Example:
<h2>This is heading 2</h2>
<h3>This is heading 3</h3>
HTML Paragraphs
HTML paragraphs are defined with the <p> tag:
Example:
<p>This is another paragraph.</p>
HTML Links
HTML links are defined with the <a> tag:
Example:
HTML Images
HTML images are defined with the <img> tag.
The source file (src), alternative text (alt), width, and height are provided as attributes:
HTML Elements:
HTML Elements
The HTML element is everything from the start tag to the end tag:
Examples of some HTML elements:
| Start tag | Element content | End tag |
|---|---|---|
| <h1> | My First Heading | </h1> |
| <p> | My first paragraph. | </p> |
| <br> | none | none |
Nested HTML Elements
HTML elements can be nested (this means that elements can contain other elements).
All HTML documents consist of nested HTML elements.
The following example contains four HTML elements (<html>, <body>, <h1> and <p>):
<!DOCTYPE html>
<html>
<body>
<h1>My First Heading</h1>
<p>My first paragraph.</p>
</body>
</html>
Example Explained
The <html> element is the root element and it defines the whole HTML document.
It has a start tag <html> and an end tag </html>.
Then, inside the <html> element there is a <body> element:
The <body> element defines the document's body.
It has a start tag <body> and an end tag </body>.
Then, inside the <body> element there are two other elements: <h1> and <p>:
<h1>My First Heading</h1>
<p>My first paragraph.</p>The <h1> element defines a heading.
It has a start tag <h1> and an end tag </h1>:
<h1>My First Heading</h1>The <p> element defines a paragraph.
It has a start tag <p> and an end tag </p>:
<p>My first paragraph.</p>Never Skip the End Tag
Some HTML elements will display correctly, even if you forget the end tag:
<body>
<p>This is a paragraph
<p>This is a paragraph
</body>
</html>
Empty HTML Elements
HTML elements with no content are called empty elements.
The <br> tag defines a line break, and is an empty element without a closing tag:
Example
<p>This is a <br> paragraph with a line break.</p>
HTML is Not Case Sensitive
HTML tags are not case sensitive: <P> means the same as <p>.
The HTML standard does not require lowercase tags, but W3C recommends lowercase in HTML, and demands lowercase for stricter document types like XHTML.
HTML Forms
An HTML form is used to collect user input. The user input is most often sent to a server for processing.
The <form> Element
The HTML <form> element is used to create an HTML form for user input:
<form>
.
form elements
.
</form>
The <form> element is a container for different types of input elements, such as: text fields, checkboxes, radio buttons, submit buttons, etc.
The <input> Element
The HTML <input> element is the most used form element.
An <input> element can be displayed in many ways, depending on the type attribute.
Here are some examples:
| Type | Description |
|---|---|
| <input type="text"> | Displays a single-line text input field |
| <input type="radio"> | Displays a radio button (for selecting one of many choices) |
| <input type="checkbox"> | Displays a checkbox (for selecting zero or more of many choices) |
| <input type="submit"> | Displays a submit button (for submitting the form) |
| <input type="button"> | Displays a clickable button |
Text Fields
The <input type="text"> defines a single-line input field for text input.
Example
A form with input fields for text:
<form>
<label for="fname">First name:</label><br>
<input type="text" id="fname" name="fname"><br>
<label for="lname">Last name:</label><br>
<input type="text" id="lname" name="lname">
</form>The <label> Element
Notice the use of the <label> element in the example above.
The <label> tag defines a label for many form elements.
The <label> element is useful for screen-reader users, because the screen-reader will read out loud the label when the user focus on the input element.
The <label> element also help users who have difficulty clicking on very small regions (such as radio buttons or checkboxes) - because when the user clicks the text within the <label> element, it toggles the radio button/checkbox.
The for attribute of the <label> tag should be equal to the id attribute of the <input> element to bind them together.
Radio Buttons
The <input type="radio"> defines a radio button.
Radio buttons let a user select ONE of a limited number of choices.
Example
A form with radio buttons:
<p>Hey plz Choose your favorite Web language:</p>
<form>
<input type="radio" id="html" name="fav_language" value="HTML">
<label for="html">HTML</label><br>
<input type="radio" id="css" name="fav_language" value="CSS">
<label for="css">CSS</label><br>
<input type="radio" id="javascript" name="fav_language" value="JavaScript">
<label for="javascript">JavaScript</label>
</form>Hey plz Choose your favorite Web language:
Checkboxes
The <input type="checkbox"> defines a checkbox.
Checkboxes let a user select ZERO or MORE options of a limited number of choices.
Example
A form with checkboxes:
<form>
<input type="checkbox" id="vehicle1" name="vehicle1" value="Bike">
<label for="vehicle1"> I have a bike</label><br>
<input type="checkbox" id="vehicle2" name="vehicle2" value="Car">
<label for="vehicle2"> I have a car</label><br>
<input type="checkbox" id="vehicle3" name="vehicle3" value="Boat">
<label for="vehicle3"> I have a boat</label>
</form>The Submit Button
The <input type="submit"> defines a button for submitting the form data to a form-handler.
The form-handler is typically a file on the server with a script for processing input data.
The form-handler is specified in the form's action attribute.
Example
A form with a submit button:
<form action="/action_page.php">
<label for="fname">First name:</label><br>
<input type="text" id="fname" name="fname" value="nil"><br>
<label for="lname">Last name:</label><br>
<input type="text" id="lname" name="lname" value="Melbern"><br><br>
<input type="submit" value="Submit">
</form>The Name Attribute for <input>
Notice that each input field must have a name attribute to be submitted.
If the name attribute is omitted, the value of the input field will not be sent at all.
Example
This example will not submit the value of the "First name" input field:
<form action="/action_page.php">
<label for="fname">First name:</label><br>
<input type="text" id="fname" value="nil"><br><br>
<input type="submit" value="Submit">
</form>HTML Form Attributes:
The Action Attribute
The action attribute defines the action to be performed when the form is submitted.
Usually, the form data is sent to a file on the server when the user clicks on the submit button.
In the example below, the form data is sent to a file called "action_page.php". This file contains a server-side script that handles the form data:
Example
On submit, send form data to "action_page.php":
<form action="/action_page.php">
<label for="fname">First name:</label><br>
<input type="text" id="fname" name="fname" value="John"><br>
<label for="lname">Last name:</label><br>
<input type="text" id="lname" name="lname" value="Doe"><br><br>
<input type="submit" value="Submit">
</form>Tip: If the action attribute is omitted, the action is set to the current page.
The Target Attribute
The target attribute specifies where to display the response that is received after submitting the form.
The target attribute can have one of the following values:
| Value | Description |
|---|---|
| _blank | The response is displayed in a new window or tab |
| _self | The response is displayed in the current window |
| _parent | The response is displayed in the parent frame |
| _top | The response is displayed in the full body of the window |
| framename | The response is displayed in a named iframe |
The default value is _self which means that the response will open in the current window.
Example
Here, the submitted result will open in a new browser tab:
<form action="/action_page.php" target="_blank">The Method Attribute
The method attribute specifies the HTTP method to be used when submitting the form data.
The form-data can be sent as URL variables (with method="get") or as HTTP post transaction (with method="post").
The default HTTP method when submitting form data is GET.
Example
This example uses the GET method when submitting the form data:
<form action="/action_page.php" method="get">Example
This example uses the POST method when submitting the form data:
<form action="/action_page.php" method="post">Notes on GET:
- Appends the form data to the URL, in name/value pairs
- NEVER use GET to send sensitive data! (the submitted form data is visible in the URL!)
- The length of a URL is limited (2048 characters)
- Useful for form submissions where a user wants to bookmark the result
- GET is good for non-secure data, like query strings in Google
Notes on POST:
- Appends the form data inside the body of the HTTP request (the submitted form data is not shown in the URL)
- POST has no size limitations, and can be used to send large amounts of data.
- Form submissions with POST cannot be bookmarked
Tip: Always use POST if the form data contains sensitive or personal information!
The Autocomplete Attribute
The autocomplete attribute specifies whether a form should have autocomplete on or off.
When autocomplete is on, the browser automatically complete values based on values that the user has entered before.
Example
A form with autocomplete on:
<form action="/action_page.php" autocomplete="on">The Novalidate Attribute
The novalidate attribute is a boolean attribute.
When present, it specifies that the form-data (input) should not be validated when submitted.
Example
A form with a novalidate attribute:
<form action="/action_page.php" novalidate>HTML Form Elements
The HTML <form> Elements
The HTML <form> element can contain one or more of the following form elements:
<input><label><select><textarea><button><fieldset><legend><datalist><output><option><optgroup>
The <input> Element
One of the most used form element is the <input> element.
The <input> element can be displayed in several ways, depending on the type attribute.
Example
<label for="fname">First name:</label>
<input type="text" id="fname" name="fname">The <label> Element
The <label> element defines a label for several form elements.
The <label> element is useful for screen-reader users, because the screen-reader will read out loud the label when the user focus on the input element.
The <label> element also help users who have difficulty clicking on very small regions (such as radio buttons or checkboxes) - because when the user clicks the text within the <label> element, it toggles the radio button/checkbox.
The for attribute of the <label> tag should be equal to the id attribute of the <input> element to bind them together.
The <select> Element
The <select> element defines a drop-down list:
Example
<label for="cars">Choose a car:</label>
<select id="cars" name="cars">
<option value="volvo">Volvo</option>
<option value="saab">Saab</option>
<option value="fiat">Fiat</option>
<option value="audi">Audi</option>
</select>The <option> elements defines an option that can be selected.
By default, the first item in the drop-down list is selected.
To define a pre-selected option, add the selected attribute to the option:
Example
<option value="fiat" selected>Fiat</option>Visible Values:
Use the size attribute to specify the number of visible values:
Example
<label for="cars">Choose a car:</label>
<select id="cars" name="cars" size="3">
<option value="volvo">Volvo</option>
<option value="saab">Saab</option>
<option value="fiat">Fiat</option>
<option value="audi">Audi</option>
</select>Allow Multiple Selections:
Use the multiple attribute to allow the user to select more than one value:
Example
<label for="cars">Choose a car:</label>
<select id="cars" name="cars" size="4" multiple>
<option value="volvo">Volvo</option>
<option value="saab">Saab</option>
<option value="fiat">Fiat</option>
<option value="audi">Audi</option>
</select>The <textarea> Element
The <textarea> element defines a multi-line input field (a text area):
Example
<textarea name="message" rows="10" cols="30">
The cat was playing in the garden.
</textarea>The rows attribute specifies the visible number of lines in a text area.
The cols attribute specifies the visible width of a text area.
This is how the HTML code above will be displayed in a browser:
You can also define the size of the text area by using CSS:Example
<textarea name="message" style="width:200px; height:600px;">
The cat was playing in the garden.
</textarea>The <button> element defines a clickable button:
Example
<button type="button" onclick="alert('Hello World!')">Click Me!</button>This is how the HTML code above will be displayed in a browser:
Note: Always specify the type attribute for the button element. Different browsers may use different default types for the button element.
The <fieldset> and <legend> Elements
The <fieldset> element is used to group related data in a form.
The <legend> element defines a caption for the <fieldset> element.
Example
<form action="/action_page.php">
<fieldset>
<legend>Personalia:</legend>
<label for="fname">First name:</label><br>
<input type="text" id="fname" name="fname" value="Johney"><br>
<label for="lname">Last name:</label><br>
<input type="text" id="lname" name="lname" value="Depp"><br><br>
<input type="submit" value="Submit">
</fieldset>
</form>This is how the HTML code above will be displayed in a browser:
The <datalist> Element
The <datalist> element specifies a list of pre-defined options for an <input> element.
Users will see a drop-down list of the pre-defined options as they input data.
The list attribute of the <input> element, must refer to the id attribute of the <datalist> element.
Example
<form action="/action_page.php">
<input list="browsers">
<datalist id="browsers">
<option value="Internet Explorer">
<option value="Firefox">
<option value="Chrome">
<option value="Opera">
<option value="Safari">
</datalist>
</form>The <output> Element
The <output> element represents the result of a calculation (like one performed by a script).
Example
Perform a calculation and show the result in an <output> element:
<form action="/action_page.php"
oninput="x.value=parseInt(a.value)+parseInt(b.value)">
0
<input type="range" id="a" name="a" value="50">
100 +
<input type="number" id="b" name="b" value="50">
=
<output name="x" for="a b"></output>
<br><br>
<input type="submit">
</form>HTML Form Elements
| Tag | Description |
|---|---|
| <form> | Defines an HTML form for user input |
| <input> | Defines an input control |
| <textarea> | Defines a multiline input control (text area) |
| <label> | Defines a label for an <input> element |
| <fieldset> | Groups related elements in a form |
| <legend> | Defines a caption for a <fieldset> element |
| <select> | Defines a drop-down list |
| <optgroup> | Defines a group of related options in a drop-down list |
| <option> | Defines an option in a drop-down list |
| <button> | Defines a clickable button |
| <datalist> | Specifies a list of pre-defined options for input controls |
| <output> | Defines the result of a calculation |
| Country | Population (in crores) | |
|---|---|---|
| INDIA | 1998 | 85 |
| 1999 | 90 | |
| 2000 | 100 | |
| USA | 1998 | 30 |
| 1999 | 35 | |
| 2000 | 40 | |
| UK | 1998 | 25 |
| 1999 | 30 | |
| 2000 | 35 | |
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