怎么判断ifame是否加载完成

var iframe = document.createElement("iframe");
	iframe.src =
		"https://etax.shaanxi.chinatax.gov.cn/app/assets/user_sx/qysmz2.html?FxAppId=5355086dce34445ab5412cb054b876b7&debug=false";
	if (iframe.attachEvent) {
		iframe.attachEvent("onload", function () {
			window.frames[0].document.getElementById('shxydm').value = '哈哈，你被我修改了。';
		});
	} else {
		iframe.onload = function () {
			window.frames[0].document.getElementById('shxydm').value = '哈哈，你被我修改了。';
		};
	}
	document.body.appendChild(iframe);