// definition
function $(s) { return new lib(s); }

function lib(s) { this.$els = document.querySelectorAll(s); }

lib.prototype.css = function(prop, val) {
    this.$els.forEach($el => ($el.style[prop] = val));
    // this is what makes it chainable
	return this;
};

lib.prototype.text = function(val) {
	if (val) {
		this.$els.forEach($el => ($el.textContent = val));
	} else {
		return Array.from(this.$els)
			.map($el => $el.textContent)
			.join(' ');
	}

	// this is what makes it chainable
	return this;
};

// usage
const texts = $('a').text();
console.log(texts);

$('a').css('color', 'red').text('this').text('no that');