main.js

function $$$(selector, rootNode=document.body) {
	const arr = []
	
	const traverser = node => {
		// 1. decline all nodes that are not elements
		if(node.nodeType !== Node.ELEMENT_NODE) {
			return
		}
		
		// 2. add the node to the array, if it matches the selector
		if(node.matches(selector)) {
			arr.push(node)
		}
		
		// 3. loop through the children
		const children = node.children
		if (children.length) {
			for(const child of children) {
				traverser(child)
			}
		}
		
		// 4. check for shadow DOM, and loop through it's children
		const shadowRoot = node.shadowRoot
		if (shadowRoot) {
			const shadowChildren = shadowRoot.children
			for(const shadowChild of shadowChildren) {
				traverser(shadowChild)
			}
		}
	}
	
	traverser(rootNode)
	
	return arr
}