Register Form validation using JavaScript 1) indexOf : starting position of Character if a match is found it returns the position of the character (starting with 0) if not returns -1 2) lastIndexOf: Checks the last position of the Character if a match is found it returns the position of the character (starting with 0) if not returns -1 3)trim(): Trim functionality removes the white space in input 4) document.getElementById.value : it read/listen the value which are typing in input Register page <! DOCTYPE html > < html lang = "en" > < head > < meta charset = "UTF-8" > < meta http-equiv = "X-UA-Compatible" content = "IE=edge" > < meta name = "viewport" content = "width=device-width, initial-scale=1.0" > < title > Communication Application </ title > < link rel = "stylesheet" href = "./Assets/css/bootstrap.min.css" >