layui的layer.confirm如何获取按钮焦点

layer.confirm('确定取消这个弹窗吗？',{
	 btn: ['确定', '取消'],
	 success:function(layero){
         //获取焦点
         var btn = layero[0].getElementsByClassName('layui-layer-btn')        
         [0].getElementsByTagName('A')[0];    
         btn.href = 'javascript:void(0)';
                btn.focus();
            },
			title:"提示"
		},function(index){
			layer.close(index);
			//你的操作
		});
	})

layer.confirm('确定取消这个弹窗吗？',{
	 btn: ['确定', '取消'],
	 success:function(layero){
         //获取焦点
         var btn = getElementsByClassName('layui-layer-btn')        
         [0].getElementsByTagName('A')[0];    
         btn.href = 'javascript:void(0)';
                btn.focus();
            },
			title:"提示"
		},function(index){
			layer.close(index);
			//你的操作
		});
	})

var getElementsByClassName = function (searchClass, node,tag) {
  var result = [];
            node = node || document;
            tag = tag || "*";
            var classes = searchClass.split(" "),
            elements = (tag === "*" && node.all) ? node.all: node.getElementsByTagName(tag),
            patterns = [],
            current,
            match;
            var i = classes.length;
            while (--i >= 0) {
                patterns.push(new RegExp("(^|\\s)" + classes[i] + "(\\s|$)"));
            }
            var j = elements.length;
            while (--j >= 0) {
                current = elements[j];
                match = false;
                for (var k = 0,
                kl = patterns.length; k < kl; k++) {
                    match = patterns[k].test(current.className);
                    if (!match) break;
                }
                if (match) result.push(current);
            }
            return result;
  }