if element is in viewport

isInViewport.js

/*!
 * if element is in viewport
 * gist.github.com/englishextra/2e9322e5eea9412f5086f7427009b903
 * stackoverflow.com/questions/123999/how-to-tell-if-a-dom-element-is-visible-in-the-current-viewport
 * jsfiddle.net/englishextra/9mwdxgez/
 * @param e an HTML element
 * var p = document.getElementById("h1") || "";
 * if(p){var g=function(_that){if(isInViewport(p))
 * {window.removeEventListener("scroll",_that);alert(1);}};
 * window.addEventListener("scroll",function h_w(){g(h_w);});}
 */
var isInViewport = function (w, d) {
	var g = function (e) {
		return (e = e ? e.getBoundingClientRect() || "" : "") ?
		0 <= e.top && 0 <= e.left && e.bottom <= (w.innerHeight ||
			d.clientHeight) && e.right <= (w.innerWidth ||
			d.clientWidth) : !0;
	};
	return g;
}(window, document.documentElement || "");
var p = document.getElementById("h1") || "";
if (p) {
	var g = function (_that) {
		if (isInViewport(p)) {
			window.removeEventListener("scroll", _that);
			alert(1);
		}
	};
	window.addEventListener("scroll", function h_w() {
		g(h_w);
	});
}