target audience

Building a custom visual (WYSIWYG) HTML editor from scratch using JavaScript relies on the contenteditable=“true” attribute combined with the modern Selection and Range APIs to format text and generate HTML source code natively.

While many legacy systems and older tutorials rely heavily on document.execCommand(), it has been completely deprecated across all modern browsers due to inconsistent behaviors. Building an enterprise-grade editor requires handling selection states and manually wrapping DOM text nodes. Step-by-Step Architecture for a Custom HTML Editor

Here is the complete roadmap, structured architecture, and functional code needed to implement a minimalist, secure HTML editor using vanilla HTML, CSS, and modern JavaScript. 1. Define UI Structure

Create a dedicated controls wrapper for the toolbar and an element with the contenteditable attribute. A textarea element hidden by default will capture and show the raw HTML code output.

Use code with caution. 2. Apply Fundamental Styles

Keep layout structures distinct. Ensure the visual editing element has defined boundaries and handles whitespace properties properly to prevent layout breaking. Use code with caution. 3. Manage Range Node Modifications

To avoid using deprecated functions, fetch active cursor selections natively using the web standard window.getSelection() and wrap text fragments directly inside element nodes. javascript

// Global function to modify selection chunks function wrapSelectionInTag(tagName) { const selection = window.getSelection(); if (!selection.rangeCount) return; // Extract highlight boundaries const range = selection.getRangeAt(0); // Guard clause against empty selections if (range.collapsed) return; // Create wrapping element const element = document.createElement(tagName); try { // Extract selected DOM objects into the tag element.appendChild(range.extractContents()); // Insert new parent back into document context range.insertNode(element); // Clear selection for user experience selection.removeAllRanges(); } catch (error) { console.error(“DOM manipulation failed”, error); } } // Handler functions bound to UI triggers function formatText(style) { if (style === ‘bold’) wrapSelectionInTag(‘strong’); if (style === ‘italic’) wrapSelectionInTag(‘em’); } function insertHeading(tag) { wrapSelectionInTag(tag); } Use code with caution. 4. Build Code Syncing Elements

To extract the resulting code string out of your interactive workspace, dynamically sync the inner element contents with your plain-text target container. javascript

const visualView = document.getElementById(‘visualCanvas’); const sourceView = document.getElementById(‘sourceCanvas’); function viewSource() { const isVisualVisible = sourceView.style.display === ‘none’; if (isVisualVisible) { // Copy the rendered HTML text string directly to textarea source sourceView.value = visualView.innerHTML; visualView.style.display = ‘none’; sourceView.style.display = ‘block’; } else { // Copy the raw markup modifications back to the canvas layout visualView.innerHTML = sourceView.value; sourceView.style.display = ‘none’; visualView.style.display = ‘block’; } } Use code with caution. Critical Engineering Guardrails

When building a vanilla layout engine to output raw HTML formatting blocks, implement these absolute development requirements:

Sanitize Inputs Continuously: Never save output values or read strings directly without validating elements. Malicious actors could copy-paste strings containing nested