JS 正则验证的一些东西

1、验证固定电话(有分机号)

String.prototype.trim =  function() {return this.replace(/^\s+|\s+$/g,"");}
function checkTel() {
    var  area_code = document.getElementById("area_code").value.trim();
    var  main_code = document.getElementById("main_code").value.trim();
    var  ext_code = document.getElementById("ext_code").value.trim();

    var telephone = "";
    if(/^\d{7,8}$/.test(main_code)) {
        if(!(/^\d{3,4}$/.test(area_code))) {
		alert("您的区号填写有误,区号应该是3~4位的数字!");
			return;
		}
		telephone = area_code+ "-" + main_code ;
		if(ext_code!= "") {
			telephone += "-" + ext_code;
		}
	}
	document.getElementById("telephone").value = telephone;
}