The id element defines a unique id for an HTML .This HTML id value can be used with CSS and JavaScript to perform certain task. In CSS, to select an element with a specific id, write hash (#) character followed by the id of the element.
HTML Id Example
<html> <head> <style> #paragraph { background-color: lightblue; color: black; text-align: center; } </style> </head> <body> <p id="paragraph">welcome to javameant</p> </body> </html>
HTML Id in Javascript
<!DOCTYPE html> <html> <body> <h1 id="myid">welcome to javameant</h1> <button onclick="result()">Change text</button> <script> function result() { document.getElementById("myid").innerHTML = "see you soon"; } </script> </body> </html>