javaScript正则截取自定义标签

var reg1 = /<span[^>]*>(.|\n)*<\/span>/gi;
var str1 = '<span>我是被删除的</span>123123';
console.log(str1.replace(reg1, ''));

var reg1 = /(<\/?font.*?>)/gi;
var reg2 = /(<\/?span.*?>)/gi;
var reg3 = /(<\/?a.*?>)/gi;
var reg4= /(<\/?font.*?>)|(<\/?span.*?>)|(<\/?a.*?>)/gi;
var str = '<span>我是被保留的</span><a href="asdasd">你好，我也是被保留的<font>我的font里的</font></a>';
console.log(str.replace(reg1, ''));
console.log(str.replace(reg2, ''));
console.log(str.replace(reg3, ''));
console.log(str.replace(reg4, ''));

var reg1 = /<span[^>]*>/gi;
var str1 = '<span style="color:red;">我是被删除的</span>123123';
console.log(str1.replace(reg1, '<span>'));