JavaScript is a programming language that's used to program HTML and web applications that run in the browser. JavaScript is mostly preferred for adding dynamic features and providing user-based interaction inside web pages. JavaScript, HTML, and CSS are among the most commonly used web technologies, and now they are also used with headless browsers. The client-side availability of the JavaScript engine has also strengthened its position in application testing and debugging.
JavaScript code can be added to HTML using <script> or embedded as a file. <script> contains programming logic with JavaScript variables, operators, functions, arrays, loops, conditions, and events, targeting the HTML Document Object Model (DOM):
<!DOCTYPE html>
<html>
<head>
<script>
function placeTitle() {
document.getElementById("innerDiv").innerHTML = "Welcome to WebScraping";
}
</script>
</head>
<body>
<div>Press the button: <p id="innerDiv"></p></div>
<br />
<button id="btnTitle" name="btnTitle" type="submit" onclick="placeTitle()">
Load Page Title!
</button>
</body>
</html>
Dynamic manipulation of HTML contents, elements, attribute values, CSS, and HTML events with accessible internal functions and programming features makes JavaScript very popular in web development. There are many web-based technologies related to JavaScript, including JSON, jQuery, AngularJS, and AJAX, among many more.
jQuery is a JavaScript library that addresses incompatibilities across browsers, providing API features to handle the HTML DOM, events, and animations.
jQuery has been acclaimed globally for providing interactivity to the web and the way JavaScript was used to code. jQuery is lightweight in comparison to JavaScript framework, it is also easy to implement, with a short and readable coding approach.
Asynchronous JavaScript and XML (AJAX) is a web development technique that uses a group of web technologies on the client side to create asynchronous web applications. JavaScript XMLHttpRequest (XHR) objects are used to execute AJAX on web pages and load page content without refreshing or reloading the page. Please visit AJAX W3Schools (https://www.w3schools.com/js/js_ajax_intro.asp) for more information on AJAX.
From a scraping point of view, a basic overview of JavaScript functionality will be valuable to understanding how a page is built or manipulated, as well as identifying the dynamic components used.