在字符串末尾追加字符串 
String.prototype.append = function (str) {
return this.concat(str);
}

删除指定索引位置的字符，索引无效将不删除任何字符 
String.prototype.deleteCharAt = function (index) {
if (index < 0 || index >= this.length) {
return this.valueOf();
}
else if (index == 0) {
return this.substring(1, this.length);
}
else if (index == this.length - 1) {
return this.substring(0, this.length - 1);
}
else {
return this.substring(0, index) + this.substring(index + 1);
}
}

删除指定索引区间的字符串 
String.prototype.deleteString = function (start, end) {
if (start == end) {
return this.deleteCharAt(start);
}
else {
if (start > end) {
var temp = start;
start = end;
end = temp;
}
if (start < 0) {
start = 0;
}
if (end > this.length - 1) {
end = this.length - 1;
}
return this.substring(0, start) + this.substring(end +1 , this.length);
}
}

检查字符串是否以subStr结尾 
String.prototype.endWith = function (subStr) {
if (subStr.length > this.length) {
return false;
}
else {
return (this.lastIndexOf(subStr) == (this.length - subStr.length)) ? true : false;
}
}

 比较两个字符串是否相等，也可以直接用 == 进行比较 
String.prototype.equal = function (str) {
if (this.length != str.length) {
return false;
}
else {
for (var i = 0; i < this.length; i++) {
if (this.charAt(i) != str.charAt(i)) {
return false;
}
}
return true;
}
}

 比较两个字符串是否相等，不区分大小写 
String.prototype.equalIgnoreCase = function (str) {
var temp1 = this.toLowerCase();
var temp2 = str.toLowerCase();
return temp1.equal(temp2);
}

 将指定的字符串插入到指定的位置后面，索引无效将直接追加到字符串的末尾 
String.prototype.insert = function (ofset, subStr) {
if (ofset < 0 || ofset >= this.length - 1) {
return this.append(subStr);
}
return this.substring(0, ofset + 1) + subStr + this.substring(ofset + 1);
}

 判断字符串是否数字串 
String.prototype.isAllNumber = function () {
for (var i = 0; i < this.length; i++) {
if (this.charAt(i) < '0' || this.charAt(i) > '9') {
return false;
}
}
return true;
}

 将字符串反序排列 
String.prototype.reserve = function () {
var temp = "";
for (var i = this.length - 1; i >= 0; i--) {
temp = temp.concat(this.charAt(i));
}
return temp;
}

 将指定的位置的字符设置为另外指定的字符或字符串.索引无效将直接返回不做任何处理 
String.prototype.setCharAt = function (index, subStr) {
if (index < 0 || index > this.length - 1) {
return this.valueOf();
}
return this.substring(0, index) + subStr + this.substring(index+1);
}

 检查字符串是否以subStr开头 
String.prototype.startWith = function (subStr) {
if (subStr.length > this.length) {
return false;
}
return (this.indexOf(subStr) == 0) ? true : false;
}

 计算长度，每个汉字占两个长度，英文字符每个占一个长度 
String.prototype.charLength = function () {
var temp = 0;
for (var i = 0; i < this.length; i++) {
if (this.charCodeAt(i) > 255) {
temp += 2;
}
else {
temp += 1;
}
}
return temp;
}
String.prototype.charLengthReg = function () {
return this.replace(/[^\x00-\xff]/g, "**").length;
}

 去掉首尾空格 
String.prototype.trim = function () {
return this.replace(/(^\s*)|(\s*$)/g, "");
}

 测试是否是数字 
String.prototype.isNumeric = function () {
var tmpFloat = parseFloat(this);
if (isNaN(tmpFloat))
return false;
var tmpLen = this.length - tmpFloat.toString().length;
return tmpFloat + "0".Repeat(tmpLen) == this;
}

 测试是否是整数 
String.prototype.isInt = function () {
if (this == "NaN")
return false;
return this == parseInt(this).toString();
}

 获取N个相同的字符串 
String.prototype.Repeat = function (num) {
var tmpArr = [];
for (var i = 0; i < num; i++) tmpArr.push(this);
return tmpArr.join("");
}

 除去左边空白  
String.prototype.LTrim = function () {
return this.replace(/^s+/g, "");
}

 除去右边空白 
String.prototype.RTrim = function () {
return this.replace(/s+$/g, "");
}

 除去两边空白  
String.prototype.trim = function () {
return this.replace(/(^s+)|(s+$)/g, "");
}

 保留数字 
String.prototype.getNum = function () {
return this.replace(/[^d]/g, "");
}

 保留字母 
String.prototype.getEn = function () {
return this.replace(/[^A-Za-z]/g, "");
}

 保留中文
String.prototype.getCn = function () {
return this.replace(/[^u4e00-u9fa5uf900-ufa2d]/g, "");
}

 得到字节长度 
String.prototype.getRealLength = function () {
return this.replace(/[^x00-xff]/g, "--").length;
}

 从左截取指定长度的字串 
String.prototype.left = function (n) {
return this.slice(0, n);
}

 从右截取指定长度的字串  
String.prototype.right = function (n) {
return this.slice(this.length - n);
}

 删除首尾空格  
String.prototype.Trim = function() { 
return this.replace(/(^\s*)|(\s*$)/g, ""); 
}

 统计指定字符出现的次数  
String.prototype.Occurs = function(ch) { 
// var re = eval("/[^"+ch+"]/g"); 
// return this.replace(re, "").length; 
return this.split(ch).length-1; 
}

 检查是否由数字组成 
String.prototype.isDigit = function() { 
var s = this.Trim(); 
return (s.replace(/\d/g, "").length == 0); 
}

 检查是否由数字字母和下划线组成 
String.prototype.isAlpha = function() { 
return (this.replace(/\w/g, "").length == 0); 
}

检查是否为数 
String.prototype.isNumber = function() { 
var s = this.Trim(); 
return (s.search(/^[+-]?[0-9.]*$/) >= 0); 
}

返回字节数
String.prototype.lenb = function() { 
return this.replace(/[^\x00-\xff]/g,"**").length; 
}

检查是否包含汉字
String.prototype.isInChinese = function() { 
return (this.length != this.replace(/[^\x00-\xff]/g,"**").length); 
}

简单的email检查 
String.prototype.isEmail = function() { 
　var strr; 
var mail = this; 
　var re = /(\w+@\w+\.\w+)(\.{0,1}\w*)(\.{0,1}\w*)/i; 
　re.exec(mail); 
　if(RegExp.$3!="" && RegExp.$3!="." && RegExp.$2!=".") 
strr = RegExp.$1+RegExp.$2+RegExp.$3; 
　else 
　　if(RegExp.$2!="" && RegExp.$2!=".") 
strr = RegExp.$1+RegExp.$2; 
　　else 
　strr = RegExp.$1; 
　return (strr==mail); 
}

简单的日期检查，成功返回日期对象  
String.prototype.isDate = function() { 
var p; 
var re1 = /(\d{4})[年./-](\d{1,2})[月./-](\d{1,2})[日]?$/; 
var re2 = /(\d{1,2})[月./-](\d{1,2})[日./-](\d{2})[年]?$/; 
var re3 = /(\d{1,2})[月./-](\d{1,2})[日./-](\d{4})[年]?$/; 
if(re1.test(this)) { 
p = re1.exec(this); 
return new Date(p[1],p[2],p[3]); 
} 
if(re2.test(this)) { 
p = re2.exec(this); 
return new Date(p[3],p[1],p[2]); 
} 
if(re3.test(this)) { 
p = re3.exec(this); 
return new Date(p[3],p[1],p[2]); 
} 
return false; 
}

检查是否有列表中的字符字符
String.prototype.isInList = function(list) { 
var re = eval("/["+list+"]/"); 
return re.test(this); 
}

系统中JS的扩展函数 

/清除两边的空格 
String.prototype.trim = function() { 
return this.replace(/(^\s*)|(\s*$)/g, ''); 
}; 

 合并多个空白为一个空白 
String.prototype.ResetBlank = function() { 
var regEx = /\s+/g; 
return this.replace(regEx, ' '); 
};

保留数字 
String.prototype.GetNum = function() { 
var regEx = /[^\d]/g; 
return this.replace(regEx, ''); 
};

保留中文 
String.prototype.GetCN = function() { 
var regEx = /[^\u4e00-\u9fa5\uf900-\ufa2d]/g; 
return this.replace(regEx, ''); 
};

String转化为Number 
String.prototype.ToInt = function() { 
return isNaN(parseInt(this)) ? this.toString() : parseInt(this); 
};

 得到字节长度 
String.prototype.GetLen = function() { 
var regEx = /^[\u4e00-\u9fa5\uf900-\ufa2d]+$/; 
if (regEx.test(this)) { 
return this.length * 2; 
} else { 
var oMatches = this.match(/[\x00-\xff]/g); 
var oLength = this.length * 2 - oMatches.length; 
return oLength; 
} 
};

 获取文件全名 
String.prototype.GetFileName = function() { 
var regEx = /^.*\/([^\/\?]*).*$/; 
return this.replace(regEx, '$1'); 
};

 数字补零 
Number.prototype.LenWithZero = function(oCount) { 
var strText = this.toString(); 
while (strText.length < oCount) { 
strText = '0' + strText; 
} 
return strText; 
};

Unicode还原 
Number.prototype.ChrW = function() { 
return String.fromCharCode(this); 
};

 数字数组由小到大排序 
Array.prototype.Min2Max = function() { 
var oValue; 
for (var i = 0; i < this.length; i++) { 
for (var j = 0; j <= i; j++) { 
if (this[i] < this[j]) { 
oValue = this[i]; 
this[i] = this[j]; 
this[j] = oValue; 
} 
} 
} 
return this; 
};

 数字数组由大到小排序 
Array.prototype.Max2Min = function() { 
var oValue; 
for (var i = 0; i < this.length; i++) { 
for (var j = 0; j <= i; j++) { 
if (this[i] > this[j]) { 
oValue = this[i]; 
this[i] = this[j]; 
this[j] = oValue; 
} 
} 
} 
return this; 
};

 获得数字数组中最大项 
Array.prototype.GetMax = function() { 
var oValue = 0; 
for (var i = 0; i < this.length; i++) { 
if (this[i] > oValue) { 
oValue = this[i]; 
} 
} 
return oValue; 
};

 获得数字数组中最小项 
Array.prototype.GetMin = function() { 
var oValue = 0; 
for (var i = 0; i < this.length; i++) { 
if (this[i] < oValue) { 
oValue = this[i]; 
} 
} 
return oValue; 
};

 获取当前时间的中文形式 
Date.prototype.GetCNDate = function() { 
var oDateText = ''; 
oDateText += this.getFullYear().LenWithZero(4) + new Number(24180).ChrW(); 
oDateText += this.getMonth().LenWithZero(2) + new Number(26376).ChrW(); 
oDateText += this.getDate().LenWithZero(2) + new Number(26085).ChrW(); 
oDateText += this.getHours().LenWithZero(2) + new Number(26102).ChrW(); 
oDateText += this.getMinutes().LenWithZero(2) + new Number(20998).ChrW(); 
oDateText += this.getSeconds().LenWithZero(2) + new Number(31186).ChrW(); 
oDateText += new Number(32).ChrW() + new Number(32).ChrW() + new Number(26143).ChrW() + new Number(26399).ChrW() + new String('26085199682010819977222352011620845').substr(this.getDay() * 5, 5).ToInt().ChrW(); 
return oDateText; 
}; 

扩展Date格式化 
Date.prototype.Format = function(format) { 
var o = { 
"M+": this.getMonth() + 1, //月份 
"d+": this.getDate(), //日 
"h+": this.getHours() % 12 == 0 ? 12 : this.getHours() % 12, //小时 
"H+": this.getHours(), //小时 
"m+": this.getMinutes(), //分 
"s+": this.getSeconds(), //秒 
"q+": Math.floor((this.getMonth() + 3) / 3), //季度 
"S": this.getMilliseconds() //毫秒 
}; 
var week = { 
"0": "\u65e5", 
"1": "\u4e00", 
"2": "\u4e8c", 
"3": "\u4e09", 
"4": "\u56db", 
"5": "\u4e94", 
"6": "\u516d" 
}; 
if (/(y+)/.test(format)) { 
format = format.replace(RegExp.$1, (this.getFullYear() + "").substr(4 - RegExp.$1.length)); 
} 
if (/(E+)/.test(format)) { 
format = format.replace(RegExp.$1, ((RegExp.$1.length > 1) ? (RegExp.$1.length > 2 ? "\u661f\u671f" : "\u5468") : "") + week[this.getDay() + ""]); 
} 
for (var k in o) { 
if (new RegExp("(" + k + ")").test(format)) { 
format = format.replace(RegExp.$1, (RegExp.$1.length == 1) ? (o[k]) : (("00" + o[k]).substr(("" + o[k]).length))); 
} 
} 
return format; 
} 
Date.prototype.Diff = function(interval, objDate) { 
//若参数不足或 objDate 不是日期类型則回传 undefined 
if (arguments.length < 2 || objDate.constructor != Date) { return undefined; } 
switch (interval) { 
//计算秒差 
case 's': return parseInt((objDate - this) / 1000); 
//计算分差 
case 'n': return parseInt((objDate - this) / 60000); 
//计算時差 
case 'h': return parseInt((objDate - this) / 3600000); 
//计算日差 
case 'd': return parseInt((objDate - this) / 86400000); 
//计算周差 
case 'w': return parseInt((objDate - this) / (86400000 * 7)); 
//计算月差 
case 'm': return (objDate.getMonth() + 1) + ((objDate.getFullYear() - this.getFullYear()) * 12) - (this.getMonth() + 1); 
//计算年差 
case 'y': return objDate.getFullYear() - this.getFullYear(); 
//输入有误 
default: return undefined; 
} 
};

 检测是否为空 
Object.prototype.IsNullOrEmpty = function() { 
var obj = this; 
var flag = false; 
if (obj == null || obj == undefined || typeof (obj) == 'undefined' || obj == '') { 
flag = true; 
} else if (typeof (obj) == 'string') { 
obj = obj.trim(); 
if (obj == '') {//为空 
flag = true; 
} else {//不为空 
obj = obj.toUpperCase(); 
if (obj == 'NULL' || obj == 'UNDEFINED' || obj == '{}') { 
flag = true; 
} 
} 
} 
else { 
flag = false; 
} 
return flag; 
};

链接: https://www.fly63.com/article/detial/1658