script.js

function update(text) {
	let result_element = document.querySelector("#highlighting-content");
	// Update code
	result_element.innerHTML = text.replace(new RegExp("&", "g"), "&amp;").replace(new RegExp("<", "g"), "&lt;"); /* Global RegExp */
	// Syntax Highlight
	Prism.highlightElement(result_element);
	// Parse markdown
	document.querySelector(".markdown-body").innerHTML = marked(text)
}

function sync_scroll(element) {
	/* Scroll result to scroll coords of event - sync with textarea */
	let result_element = document.querySelector("#highlighting");
	// Get and set x and y
	result_element.scrollTop = element.scrollTop;
	result_element.scrollLeft = element.scrollLeft;
}

function check_tab(element, event) {
	let code = element.value;
	if (event.key == "Tab") {
		/* Tab key pressed */
		event.preventDefault(); // stop normal
		let before_tab = code.slice(0, element.selectionStart); // text before tab
		let after_tab = code.slice(element.selectionEnd, element.value.length); // text after tab
		let cursor_pos = element.selectionEnd + 2; // after tab placed, where cursor moves to - 2 for 2 spaces
		element.value = before_tab + "  " + after_tab; // add tab char - 2 spaces
		// move cursor
		element.selectionStart = cursor_pos;
		element.selectionEnd = cursor_pos;
	}
}