JavaScript 常用的技术(陆续更新)

截取字符串(指定长度)

var str = "abc-110001";

//str.substring(起始位置(0开始),截取的长度)

str.substring(0,4);

//运行结果:abc-

把字符串转换成数字

var str = "0001";

var newValues = parseInt(str);

使用正则表达式判断数字

var gs_reg = /^[0-9]*$/;

if(gs_reg.test("as"))
{
　alert("I am is numeric!");
}
else
{
　alert("Sorry, I am is not numeric!");
}

Javascript IsNaN()函数

isNaN() 函数用于检查其参数是否是非数字值。
检查数字是否非法：
<script>

document.write(isNaN(123));
document.write(isNaN(-1.23));
document.write(isNaN(5-2));
document.write(isNaN(0));
document.write(isNaN("Hello"));
document.write(isNaN("2005/12/12"));

</script>
输出：
false
false
false
false
true
true

如果返回值是false 说明这个结果是数字来的, 如果是true 那么这个结果不是有效的数字

　js 得到当前季度

Date.prototype.getQuarter = function() {
        var month = this.getMonth();
        if(month  < 3) {
            return '第一季度';
        }else if(month < 6) {
            return '第二季度';
        }else if(month <9) {
            return '第三季度';
        }else if(month <12) {
            return '第四季度';
        }
};

　　

/**
* 获取本周、本季度、本月、上月的开端日期、停止日期
*/
var now = new Date(); //当前日期
var nowDayOfWeek = now.getDay(); //今天本周的第几天
var nowDay = now.getDate(); //当前日
var nowMonth = now.getMonth(); //当前月
var nowYear = now.getYear(); //当前年
nowYear += (nowYear < 2000) ? 1900 : 0; // 

var lastMonthDate = new Date(); //上月日期
lastMonthDate.setDate(1);
lastMonthDate.setMonth(lastMonthDate.getMonth()-1);
var lastYear = lastMonthDate.getYear();
var lastMonth = lastMonthDate.getMonth(); 

//格局化日期：yyyy-MM-dd
function formatDate(date) {
var myyear = date.getFullYear();
var mymonth = date.getMonth()+1;
var myweekday = date.getDate(); 

if(mymonth < 10){
mymonth = "0" + mymonth;
}
if(myweekday < 10){
myweekday = "0" + myweekday;
}
return (myyear+"-"+mymonth + "-" + myweekday);
} 

//获得某月的天数
function getMonthDays(myMonth){
var monthStartDate = new Date(nowYear, myMonth, 1);
var monthEndDate = new Date(nowYear, myMonth + 1, 1);
var days = (monthEndDate - monthStartDate)/(1000 * 60 * 60 * 24);
return days;
} 

//获得本季度的开端月份
function getQuarterStartMonth(){
var quarterStartMonth = 0;
if(nowMonth<3){
quarterStartMonth = 0;
}
if(2<nowMonth && nowMonth<6){
quarterStartMonth = 3;
}
if(5<nowMonth && nowMonth<9){
quarterStartMonth = 6;
}
if(nowMonth>8){
quarterStartMonth = 9;
}
return quarterStartMonth;
} 

//获得本周的开端日期
function getWeekStartDate() {
var weekStartDate = new Date(nowYear, nowMonth, nowDay - nowDayOfWeek);
return formatDate(weekStartDate);
} 

//获得本周的停止日期
function getWeekEndDate() {
var weekEndDate = new Date(nowYear, nowMonth, nowDay + (6 - nowDayOfWeek));
return formatDate(weekEndDate);
} 

//获得本月的开端日期
function getMonthStartDate(){
var monthStartDate = new Date(nowYear, nowMonth, 1);
return formatDate(monthStartDate);
} 

//获得本月的停止日期
function getMonthEndDate(){
var monthEndDate = new Date(nowYear, nowMonth, getMonthDays(nowMonth));
return formatDate(monthEndDate);
} 

//获得上月开端时候
function getLastMonthStartDate(){
var lastMonthStartDate = new Date(nowYear, lastMonth, 1);
return formatDate(lastMonthStartDate);
} 

//获得上月停止时候
function getLastMonthEndDate(){
var lastMonthEndDate = new Date(nowYear, lastMonth, getMonthDays(lastMonth));
return formatDate(lastMonthEndDate);
} 

//获得本季度的开端日期
function getQuarterStartDate(){ 

var quarterStartDate = new Date(nowYear, getQuarterStartMonth(), 1);
return formatDate(quarterStartDate);
} 

//或的本季度的停止日期
function getQuarterEndDate(){
var quarterEndMonth = getQuarterStartMonth() + 2;
var quarterStartDate = new Date(nowYear, quarterEndMonth, getMonthDays(quarterEndMonth));
return formatDate(quarterStartDate);
}