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); 
}