alert("18723568888".replace(/(?=(\d{4})+$)/g,"-"));//横线
alert("18723568888".replace(/(?=(\d{4})+$)/g,"-")); //空格
alert("18723568888".replace(/(?=(\d{4})+$)/g,"-"));
alert("18723568888".replace(/(?=(\d{4})+$)/g,"-"));//横线
alert("18723568888".replace(/(?=(\d{4})+$)/g,"-")); //空格
alert("18723568888".replace(/(?=(\d{4})+$)/g,"-"));