Here you can find the source of toggle()
HTMLElement.prototype.toggle = function toggle() { this.style.visibility = (this.style.visibility === "hidden") ? "visible" : "hidden"; };
Element.prototype.toggleAttribute = function(name, value = "") { if ( this.hasAttribute(name) ) { this.removeAttribute(name); else { this.setAttribute(name, value); String.prototype.ucFirst = function() { ...
Element.prototype.toggleDisplay = function() { if (this.style.display != "") this.style.display = ""; else this.style.display = "none";