The negative lookahead technique for RegEx can be employed to identify open tags while disregarding XHTML self-closing tags.
Regular Expression (RegEx) serves as a crucial resource for text manipulation. In the realm of HTML, a significant hurdle is identifying open tags while omitting self-closing tags. Various strategies, including Negative Lookahead, HTML Tags Whitelisting, and DOM Parsing, are utilized for this task. This blog will elaborately cover these strategies.
Open tags represent HTML components that require a closing tag to finish. The content or elements are encapsulated between these tags. Examples include: <div></div>, <span></span>, <p></p>, etc.
Self-contained tags are those that do not necessitate a closing tag. They function as independent units that do not encapsulate any content. Examples consist of: <img src=””/>, <br/>, <input type=””/>.
When utilizing regular expressions to find open tags, be sure to exclude self-contained tags. Misinterpreting them as open tags can lead to parsing errors, inaccurate selections, or unforeseen behaviors.
Techniques for RegEx to Identify Open HTML Tags Excluding Self-contained XHTML Tags
Negative Lookahead, HTML Tags Whitelisting, and DOM Parsing are applied to match open tags while excluding XHTML self-closing tags. Below, we will go into these strategies further:
Technique 1: Utilizing the Negative Look-Ahead Technique
A RegEx pattern can be constructed to ensure that the match does not conclude with />, thus preventing the capture of self-contained tags.
Example:
Html
Code Copied!
var isMobile = window.innerWidth “);
editor63145.setValue(decodedContent); // Set the default text
editor63145.clearSelection();
editor63145.setOptions({
maxLines: Infinity
});
function decodeHTML63145(input) {
var doc = new DOMParser().parseFromString(input, “text/html”);
return doc.documentElement.textContent;
}
// Function to copy code to clipboard
function copyCodeToClipboard63145() {
const code = editor63145.getValue(); // Get code from the editor
navigator.clipboard.writeText(code).then(() => {
jQuery(“.maineditor63145 .copymessage”).show();
setTimeout(function() {
jQuery(“.maineditor63145 .copymessage”).hide();
}, 2000);
}).catch(err => {
console.error(“Error copying code: “, err);
});
}
function closeoutput63145() {
var code = editor63145.getSession().getValue();
jQuery(“.maineditor63145 .code-editor-output”).hide();
}
// Attach event listeners to the buttons
document.getElementById(“copyBtn63145”).addEventListener(“click”, copyCodeToClipboard63145);
document.getElementById(“runBtn63145”).addEventListener(“click”, runCode63145);
“`html
document.getElementById(“closeoutputBtn63145”).addEventListener(“click”, closeoutput63145);
Result:
Clarification: Employ the RegEx pattern <([a-zA-Z]+)(?:(?!/>)[^>])*?> which exclusively selects the opening tags, thus evading tags that self-close like <img />, <br />, and <input />.
Approach 2: Implementing a Whitelist of HTML Tags
You can compile a manual list of open tags such as div, span, and p tags, permitting only matches from that compilation.
Sample:
Html
Code Copied!
var isMobile = window.innerWidth “);
editor22479.setValue(decodedContent); // Initialize with default text
editor22479.clearSelection();
editor22479.setOptions({
maxLines: Infinity
});
function decodeHTML22479(input) {
var doc = new DOMParser().parseFromString(input, “text/html”);
return doc.documentElement.textContent;
}
// Function to duplicate code to clipboard
function copyCodeToClipboard22479() {
const code = editor22479.getValue(); // Obtain code from the editor
navigator.clipboard.writeText(code).then(() => {
// alert(“Code copied to clipboard!”);
function closeoutput22479() {
var code = editor22479.getSession().getValue();
jQuery(".maineditor22479 .code-editor-output").hide();
}
// Bind event listeners to the buttons
document.getElementById("copyBtn22479").addEventListener("click", copyCodeToClipboard22479);
document.getElementById("runBtn22479").addEventListener("click", runCode22479);
document.getElementById("closeoutputBtn22479").addEventListener("click", closeoutput22479);
Result:
Clarification: This snippet allows you to verify the pattern that corresponds to ‘div’, ‘p’, ‘h1’, ‘h2’, and <h3>. Consequently, self-closing tags can be avoided. You may adjust allowedTags according to your specifications.
This script validates the pattern that solely corresponds to ‘div’, ‘p’, ‘h1’, ‘h2’, and <h3>. It effectively prevents all self-closing tags. The allowedTags array can be modified based on your needs.
Approach 3: Utilizing DOM Parsing in JavaScript
You can take advantage of JavaScript's DOMParser API to analyze the structure of the document and expunge all self-closing tags.
Sample:
Html
Code Copied!
``````html
var isMobile = window.innerWidth {n if (node.nodeType === 1) { // Verify if it's an element noden let tagName = node.tagName.toLowerCase();n if (selfClosingTags.includes(tagName)) {n openTags.push(`&&cl;${tagName}&&cg;`);n }n }n });n document.getElementById("domOutput").textContent = openTags.join("n");n }n &&cl;/script&&cg;n&&cl;/body&&cg;n&&cl;/html&&cg;n");
function closeoutput60206() {
var code = editor60206.getSession().getValue();
jQuery(".maineditor60206 .code-editor-output").hide();
}
// Attach event listeners to the buttons
document.getElementById("copyBtn60206").addEventListener("click", copyCodeToClipboard60206);
document.getElementById("runBtn60206").addEventListener("click", runCode60206);
document.getElementById("closeoutputBtn60206").addEventListener("click", closeoutput60206);
Result:
Clarification: You can utilize the DOMParser to analyze and extract solely the opening tags, while excluding self-closing tags like <img /> and <input />.
Summary
Employing RegEx in functions such as Negative Lookahead, HTML Tag Whitelisting, and DOM Parsing allows for the capture of opening tags excluding the XHTML self-contained tags. The aforementioned techniques are suitable for this objective. Depending on your requirements, feel free to select any of these methods.
To provide the best experiences, we use technologies like cookies to store and/or access device information. Consenting to these technologies will allow us to process data such as browsing behavior or unique IDs on this site. Not consenting or withdrawing consent, may adversely affect certain features and functions.
Functional
Always active
The technical storage or access is strictly necessary for the legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user, or for the sole purpose of carrying out the transmission of a communication over an electronic communications network.
Preferences
The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user.
Statistics
The technical storage or access that is used exclusively for statistical purposes.The technical storage or access that is used exclusively for anonymous statistical purposes. Without a subpoena, voluntary compliance on the part of your Internet Service Provider, or additional records from a third party, information stored or retrieved for this purpose alone cannot usually be used to identify you.
Marketing
The technical storage or access is required to create user profiles to send advertising, or to track the user on a website or across several websites for similar marketing purposes.
