Working with DOM Elements

The DOM (Document Object Model) is a programming interface for web documents. It represents the structure of a webpage as a tree of objects, allowing JavaScript to interact with and manipulate HTML elements. This chapter will take you through everything you need to know about working with DOM elements, from the basics to advanced concepts.

Introduction to the DOM

What is the DOM?

  • The DOM is a representation of an HTML or XML document as a tree of nodes.
  • Each element, attribute, and piece of text in HTML becomes a node in the DOM.

Why is the DOM Important?

  • The DOM allows JavaScript to dynamically update content, structure, and style of a webpage.
  • It enables event handling (e.g., clicks, mouse movements) and interaction with the browser.

How to Access the DOM in JavaScript

The document Object

  • The document object is the entry point for accessing the DOM. It provides methods and properties to work with DOM elements.

Example

				
					<!DOCTYPE html>
<html>
<head>
  <title>DOM Example</title>
</head>
<body>
  <h1 id="title">Hello, DOM!</h1> <script type="litespeed/javascript">console.log(document.title)</script> <script data-no-optimize="1">window.lazyLoadOptions=Object.assign({},{threshold:300},window.lazyLoadOptions||{});!function(t,e){"object"==typeof exports&&"undefined"!=typeof module?module.exports=e():"function"==typeof define&&define.amd?define(e):(t="undefined"!=typeof globalThis?globalThis:t||self).LazyLoad=e()}(this,function(){"use strict";function e(){return(e=Object.assign||function(t){for(var e=1;e<arguments.length;e++){var n,a=arguments[e];for(n in a)Object.prototype.hasOwnProperty.call(a,n)&&(t[n]=a[n])}return t}).apply(this,arguments)}function o(t){return e({},at,t)}function l(t,e){return t.getAttribute(gt+e)}function c(t){return l(t,vt)}function s(t,e){return function(t,e,n){e=gt+e;null!==n?t.setAttribute(e,n):t.removeAttribute(e)}(t,vt,e)}function i(t){return s(t,null),0}function r(t){return null===c(t)}function u(t){return c(t)===_t}function d(t,e,n,a){t&&(void 0===a?void 0===n?t(e):t(e,n):t(e,n,a))}function f(t,e){et?t.classList.add(e):t.className+=(t.className?" ":"")+e}function _(t,e){et?t.classList.remove(e):t.className=t.className.replace(new RegExp("(^|\\s+)"+e+"(\\s+|$)")," ").replace(/^\s+/,"").replace(/\s+$/,"")}function g(t){return t.llTempImage}function v(t,e){!e||(e=e._observer)&&e.unobserve(t)}function b(t,e){t&&(t.loadingCount+=e)}function p(t,e){t&&(t.toLoadCount=e)}function n(t){for(var e,n=[],a=0;e=t.children[a];a+=1)"SOURCE"===e.tagName&&n.push(e);return n}function h(t,e){(t=t.parentNode)&&"PICTURE"===t.tagName&&n(t).forEach(e)}function a(t,e){n(t).forEach(e)}function m(t){return!!t[lt]}function E(t){return t[lt]}function I(t){return delete t[lt]}function y(e,t){var n;m(e)||(n={},t.forEach(function(t){n[t]=e.getAttribute(t)}),e[lt]=n)}function L(a,t){var o;m(a)&&(o=E(a),t.forEach(function(t){var e,n;e=a,(t=o[n=t])?e.setAttribute(n,t):e.removeAttribute(n)}))}function k(t,e,n){f(t,e.class_loading),s(t,st),n&&(b(n,1),d(e.callback_loading,t,n))}function A(t,e,n){n&&t.setAttribute(e,n)}function O(t,e){A(t,rt,l(t,e.data_sizes)),A(t,it,l(t,e.data_srcset)),A(t,ot,l(t,e.data_src))}function w(t,e,n){var a=l(t,e.data_bg_multi),o=l(t,e.data_bg_multi_hidpi);(a=nt&&o?o:a)&&(t.style.backgroundImage=a,n=n,f(t=t,(e=e).class_applied),s(t,dt),n&&(e.unobserve_completed&&v(t,e),d(e.callback_applied,t,n)))}function x(t,e){!e||0<e.loadingCount||0<e.toLoadCount||d(t.callback_finish,e)}function M(t,e,n){t.addEventListener(e,n),t.llEvLisnrs[e]=n}function N(t){return!!t.llEvLisnrs}function z(t){if(N(t)){var e,n,a=t.llEvLisnrs;for(e in a){var o=a[e];n=e,o=o,t.removeEventListener(n,o)}delete t.llEvLisnrs}}function C(t,e,n){var a;delete t.llTempImage,b(n,-1),(a=n)&&--a.toLoadCount,_(t,e.class_loading),e.unobserve_completed&&v(t,n)}function R(i,r,c){var l=g(i)||i;N(l)||function(t,e,n){N(t)||(t.llEvLisnrs={});var a="VIDEO"===t.tagName?"loadeddata":"load";M(t,a,e),M(t,"error",n)}(l,function(t){var e,n,a,o;n=r,a=c,o=u(e=i),C(e,n,a),f(e,n.class_loaded),s(e,ut),d(n.callback_loaded,e,a),o||x(n,a),z(l)},function(t){var e,n,a,o;n=r,a=c,o=u(e=i),C(e,n,a),f(e,n.class_error),s(e,ft),d(n.callback_error,e,a),o||x(n,a),z(l)})}function T(t,e,n){var a,o,i,r,c;t.llTempImage=document.createElement("IMG"),R(t,e,n),m(c=t)||(c[lt]={backgroundImage:c.style.backgroundImage}),i=n,r=l(a=t,(o=e).data_bg),c=l(a,o.data_bg_hidpi),(r=nt&&c?c:r)&&(a.style.backgroundImage='url("'.concat(r,'")'),g(a).setAttribute(ot,r),k(a,o,i)),w(t,e,n)}function G(t,e,n){var a;R(t,e,n),a=e,e=n,(t=Et[(n=t).tagName])&&(t(n,a),k(n,a,e))}function D(t,e,n){var a;a=t,(-1<It.indexOf(a.tagName)?G:T)(t,e,n)}function S(t,e,n){var a;t.setAttribute("loading","lazy"),R(t,e,n),a=e,(e=Et[(n=t).tagName])&&e(n,a),s(t,_t)}function V(t){t.removeAttribute(ot),t.removeAttribute(it),t.removeAttribute(rt)}function j(t){h(t,function(t){L(t,mt)}),L(t,mt)}function F(t){var e;(e=yt[t.tagName])?e(t):m(e=t)&&(t=E(e),e.style.backgroundImage=t.backgroundImage)}function P(t,e){var n;F(t),n=e,r(e=t)||u(e)||(_(e,n.class_entered),_(e,n.class_exited),_(e,n.class_applied),_(e,n.class_loading),_(e,n.class_loaded),_(e,n.class_error)),i(t),I(t)}function U(t,e,n,a){var o;n.cancel_on_exit&&(c(t)!==st||"IMG"===t.tagName&&(z(t),h(o=t,function(t){V(t)}),V(o),j(t),_(t,n.class_loading),b(a,-1),i(t),d(n.callback_cancel,t,e,a)))}function $(t,e,n,a){var o,i,r=(i=t,0<=bt.indexOf(c(i)));s(t,"entered"),f(t,n.class_entered),_(t,n.class_exited),o=t,i=a,n.unobserve_entered&&v(o,i),d(n.callback_enter,t,e,a),r||D(t,n,a)}function q(t){return t.use_native&&"loading"in HTMLImageElement.prototype}function H(t,o,i){t.forEach(function(t){return(a=t).isIntersecting||0<a.intersectionRatio?$(t.target,t,o,i):(e=t.target,n=t,a=o,t=i,void(r(e)||(f(e,a.class_exited),U(e,n,a,t),d(a.callback_exit,e,n,t))));var e,n,a})}function B(e,n){var t;tt&&!q(e)&&(n._observer=new IntersectionObserver(function(t){H(t,e,n)},{root:(t=e).container===document?null:t.container,rootMargin:t.thresholds||t.threshold+"px"}))}function J(t){return Array.prototype.slice.call(t)}function K(t){return t.container.querySelectorAll(t.elements_selector)}function Q(t){return c(t)===ft}function W(t,e){return e=t||K(e),J(e).filter(r)}function X(e,t){var n;(n=K(e),J(n).filter(Q)).forEach(function(t){_(t,e.class_error),i(t)}),t.update()}function t(t,e){var n,a,t=o(t);this._settings=t,this.loadingCount=0,B(t,this),n=t,a=this,Y&&window.addEventListener("online",function(){X(n,a)}),this.update(e)}var Y="undefined"!=typeof window,Z=Y&&!("onscroll"in window)||"undefined"!=typeof navigator&&/(gle|ing|ro)bot|crawl|spider/i.test(navigator.userAgent),tt=Y&&"IntersectionObserver"in window,et=Y&&"classList"in document.createElement("p"),nt=Y&&1<window.devicePixelRatio,at={elements_selector:".lazy",container:Z||Y?document:null,threshold:300,thresholds:null,data_src:"src",data_srcset:"srcset",data_sizes:"sizes",data_bg:"bg",data_bg_hidpi:"bg-hidpi",data_bg_multi:"bg-multi",data_bg_multi_hidpi:"bg-multi-hidpi",data_poster:"poster",class_applied:"applied",class_loading:"litespeed-loading",class_loaded:"litespeed-loaded",class_error:"error",class_entered:"entered",class_exited:"exited",unobserve_completed:!0,unobserve_entered:!1,cancel_on_exit:!0,callback_enter:null,callback_exit:null,callback_applied:null,callback_loading:null,callback_loaded:null,callback_error:null,callback_finish:null,callback_cancel:null,use_native:!1},ot="src",it="srcset",rt="sizes",ct="poster",lt="llOriginalAttrs",st="loading",ut="loaded",dt="applied",ft="error",_t="native",gt="data-",vt="ll-status",bt=[st,ut,dt,ft],pt=[ot],ht=[ot,ct],mt=[ot,it,rt],Et={IMG:function(t,e){h(t,function(t){y(t,mt),O(t,e)}),y(t,mt),O(t,e)},IFRAME:function(t,e){y(t,pt),A(t,ot,l(t,e.data_src))},VIDEO:function(t,e){a(t,function(t){y(t,pt),A(t,ot,l(t,e.data_src))}),y(t,ht),A(t,ct,l(t,e.data_poster)),A(t,ot,l(t,e.data_src)),t.load()}},It=["IMG","IFRAME","VIDEO"],yt={IMG:j,IFRAME:function(t){L(t,pt)},VIDEO:function(t){a(t,function(t){L(t,pt)}),L(t,ht),t.load()}},Lt=["IMG","IFRAME","VIDEO"];return t.prototype={update:function(t){var e,n,a,o=this._settings,i=W(t,o);{if(p(this,i.length),!Z&&tt)return q(o)?(e=o,n=this,i.forEach(function(t){-1!==Lt.indexOf(t.tagName)&&S(t,e,n)}),void p(n,0)):(t=this._observer,o=i,t.disconnect(),a=t,void o.forEach(function(t){a.observe(t)}));this.loadAll(i)}},destroy:function(){this._observer&&this._observer.disconnect(),K(this._settings).forEach(function(t){I(t)}),delete this._observer,delete this._settings,delete this.loadingCount,delete this.toLoadCount},loadAll:function(t){var e=this,n=this._settings;W(t,n).forEach(function(t){v(t,e),D(t,n,e)})},restoreAll:function(){var e=this._settings;K(e).forEach(function(t){P(t,e)})}},t.load=function(t,e){e=o(e);D(t,e)},t.resetStatus=function(t){i(t)},t}),function(t,e){"use strict";function n(){e.body.classList.add("litespeed_lazyloaded")}function a(){console.log("[LiteSpeed] Start Lazy Load"),o=new LazyLoad(Object.assign({},t.lazyLoadOptions||{},{elements_selector:"[data-lazyloaded]",callback_finish:n})),i=function(){o.update()},t.MutationObserver&&new MutationObserver(i).observe(e.documentElement,{childList:!0,subtree:!0,attributes:!0})}var o,i;t.addEventListener?t.addEventListener("load",a,!1):t.attachEvent("onload",a)}(window,document);</script><script data-no-optimize="1">window.litespeed_ui_events=window.litespeed_ui_events||["mouseover","click","keydown","wheel","touchmove","touchstart"];var urlCreator=window.URL||window.webkitURL;function litespeed_load_delayed_js_force(){console.log("[LiteSpeed] Start Load JS Delayed"),litespeed_ui_events.forEach(e=>{window.removeEventListener(e,litespeed_load_delayed_js_force,{passive:!0})}),document.querySelectorAll("iframe[data-litespeed-src]").forEach(e=>{e.setAttribute("src",e.getAttribute("data-litespeed-src"))}),"loading"==document.readyState?window.addEventListener("DOMContentLoaded",litespeed_load_delayed_js):litespeed_load_delayed_js()}litespeed_ui_events.forEach(e=>{window.addEventListener(e,litespeed_load_delayed_js_force,{passive:!0})});async function litespeed_load_delayed_js(){let t=[];for(var d in document.querySelectorAll('script[type="litespeed/javascript"]').forEach(e=>{t.push(e)}),t)await new Promise(e=>litespeed_load_one(t[d],e));document.dispatchEvent(new Event("DOMContentLiteSpeedLoaded")),window.dispatchEvent(new Event("DOMContentLiteSpeedLoaded"))}function litespeed_load_one(t,e){console.log("[LiteSpeed] Load ",t);var d=document.createElement("script");d.addEventListener("load",e),d.addEventListener("error",e),t.getAttributeNames().forEach(e=>{"type"!=e&&d.setAttribute("data-src"==e?"src":e,t.getAttribute(e))});let a=!(d.type="text/javascript");!d.src&&t.textContent&&(d.src=litespeed_inline2src(t.textContent),a=!0),t.after(d),t.remove(),a&&e()}function litespeed_inline2src(t){try{var d=urlCreator.createObjectURL(new Blob([t.replace(/^(?:<!--)?(.*?)(?:-->)?$/gm,"$1")],{type:"text/javascript"}))}catch(e){d="data:text/javascript;base64,"+btoa(t.replace(/^(?:<!--)?(.*?)(?:-->)?$/gm,"$1"))}return d}</script><script data-no-optimize="1">var litespeed_vary=document.cookie.replace(/(?:(?:^|.*;\s*)_lscache_vary\s*\=\s*([^;]*).*$)|^.*$/,"");litespeed_vary||fetch("/wp-content/plugins/litespeed-cache/guest.vary.php",{method:"POST",cache:"no-cache",redirect:"follow"}).then(e=>e.json()).then(e=>{console.log(e),e.hasOwnProperty("reload")&&"yes"==e.reload&&(sessionStorage.setItem("litespeed_docref",document.referrer),window.location.reload(!0))});</script><script data-optimized="1" type="litespeed/javascript" data-src="https://diginode.in/wp-content/litespeed/js/5ad5da7e80e1ecf64f3d75c5dab7ddb4.js?ver=8169a"></script></body>
</html>

Selecting DOM Elements

You can select elements using various methods provided by the document object.

getElementById

  • Selects an element by its id attribute.
				
					<p id="example">This is an example.</p> <script type="litespeed/javascript">const element=document.getElementById('example');console.log(element.textContent)</script>

getElementsByClassName

  • Selects all elements with a specific class.
				
					<div class="item">Item 1</div>
<div class="item">Item 2</div> <script type="litespeed/javascript">const items=document.getElementsByClassName('item');console.log(items[0].textContent)</script>

getElementsByTagName

  • Selects all elements with a specific tag name.
				
					<ul>
  <li>Apple</li>
  <li>Banana</li>
</ul> <script type="litespeed/javascript">const listItems=document.getElementsByTagName('li');console.log(listItems.length)</script>

querySelector and querySelectorAll

  • Use CSS selectors to find elements.

querySelector:

				
					<p class="paragraph">First Paragraph</p>
<p class="paragraph">Second Paragraph</p> <script type="litespeed/javascript">const firstParagraph=document.querySelector('.paragraph');console.log(firstParagraph.textContent)</script>

querySelectorAll:

				
					<p class="paragraph">First Paragraph</p>
<p class="paragraph">Second Paragraph</p> <script type="litespeed/javascript">const allParagraphs=document.querySelectorAll('.paragraph');console.log(allParagraphs[1].textContent)</script>

Modifying DOM Elements

Once you have selected an element, you can modify its content, attributes, and styles.

Changing Content

  • Use textContent or innerHTML to update content.

textContent:

				
					<p id="demo">Old Text</p> <script type="litespeed/javascript">const paragraph=document.getElementById('demo');paragraph.textContent='New Text'</script>

innerHTML:

				
					<div id="container">Old HTML</div> <script type="litespeed/javascript">const container=document.getElementById('container');container.innerHTML='<strong>New HTML</strong>'</script>

Changing Attributes

You can get or set attributes using getAttribute and setAttribute.

Example:

				
					<img data-lazyloaded="1" src="data:image/gif;base64,R0lGODdhAQABAPAAAMPDwwAAACwAAAAAAQABAAACAkQBADs=" decoding="async" id="myImage" data-src="old.jpg" alt="Old Image" title="Working with DOM Elements 1"> <script type="litespeed/javascript">const image=document.getElementById('myImage');image.setAttribute('src','new.jpg');console.log(image.getAttribute('alt'))</script>

Modifying Styles

  • Use the style property to change CSS dynamically.

Example:

				
					<div id="box" style="width: 100px; height: 100px; background: red;"></div> <script type="litespeed/javascript">const box=document.getElementById('box');box.style.backgroundColor='blue';box.style.border='2px solid black'</script>

Event Handling

Events let you add interactivity to your webpage.

Adding Event Listeners

Use addEventListener to attach events.

Example:

				
					<button id="btn">Click Me</button> <script type="litespeed/javascript">const button=document.getElementById('btn');button.addEventListener('click',()=>{alert('Button was clicked!')})</script>

Traversing the DOM

Navigate between parent, child, and sibling nodes.

Parent and Child Nodes

				
					<div id="parent">
  <p id="child">Child Element</p>
</div> <script type="litespeed/javascript">const child=document.getElementById('child');console.log(child.parentNode.id)</script>

Sibling Nodes

				
					<ul>
  <li id="item1">Item 1</li>
  <li id="item2">Item 2</li>
</ul> <script type="litespeed/javascript">const item1=document.getElementById('item1');console.log(item1.nextElementSibling.textContent)</script>

Advanced Topics

Cloning Nodes

Use cloneNode to duplicate an element.

Example:

				
					<div id="original">Original Node</div> <script type="litespeed/javascript">const original=document.getElementById('original');const clone=original.cloneNode(!0);document.body.appendChild(clone)</script>

Templates

Templates let you define reusable content.

Example:

				
					<template id="template">
  <p>Template Content</p>
</template> <script type="litespeed/javascript">const template=document.getElementById('template').content.cloneNode(!0);document.body.appendChild(template)</script>

Working with DOM elements is a fundamental skill for JavaScript developers. By understanding how to select, modify, traverse, and manipulate DOM elements, you can create dynamic and interactive web applications. Mastering these concepts will empower you to build user-friendly, responsive websites. Happy coding !❤️

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